Rahul Joshi 
This workflow corresponds to n8n.io template #15694 — we link there as the canonical source.
This workflow follows the Gmail → Gmail Trigger recipe pattern — see all workflows that pair these two integrations.
The workflow JSON
Copy or download the full n8n JSON below. Paste it into a new n8n workflow, add your credentials, activate. Full import guide →
{
"id": "OpKu0lBYH8fjHJZw",
"meta": {
"templateCredsSetupCompleted": true
},
"name": "Invoice OCR Pipeline Automation",
"tags": [],
"nodes": [
{
"id": "38181a69-951e-45f4-8cd0-ea1965203ffa",
"name": "\ud83d\udce7 Gmail \u2014 Watch for Invoice Emails",
"type": "n8n-nodes-base.gmailTrigger",
"notes": "Polls Gmail every minute for unread emails with 'invoice' in subject. Captures all attachments as binary fields.",
"position": [
-2240,
896
],
"parameters": {
"simple": false,
"filters": {
"sender": "user@example.com"
},
"options": {},
"pollTimes": {
"item": [
{
"mode": "everyMinute"
}
]
}
},
"credentials": {
"gmailOAuth2": {
"name": "<your credential>"
}
},
"typeVersion": 1
},
{
"id": "9bf735e6-8d44-4b76-91ee-0445280fd7e5",
"name": "\u2753 Has PDF Attachment?",
"type": "n8n-nodes-base.if",
"notes": "Only continue if email has PDF/image attachments. Emails without attachments are silently skipped.",
"position": [
-1824,
896
],
"parameters": {
"options": {},
"conditions": {
"options": {
"version": 1,
"leftValue": "",
"caseSensitive": true,
"typeValidation": "strict"
},
"combinator": "and",
"conditions": [
{
"id": "cond-001",
"operator": {
"type": "boolean",
"operation": "true",
"singleValue": true
},
"leftValue": "={{ $json.has_attachment }}",
"rightValue": "true"
}
]
}
},
"typeVersion": 2
},
{
"id": "02e15b78-e0e2-4c0f-ae91-f5801ba600a3",
"name": "\ud83d\udcce Gmail \u2014 Download Invoice Attachment",
"type": "n8n-nodes-base.gmail",
"notes": "Downloads the full attachment binary so Mistral OCR can process it.",
"position": [
-1584,
832
],
"parameters": {
"simple": false,
"options": {
"downloadAttachments": true
},
"messageId": "={{ $json.id }}",
"operation": "get"
},
"credentials": {
"gmailOAuth2": {
"name": "<your credential>"
}
},
"typeVersion": 2.1
},
{
"id": "a8420d4d-1554-40b1-8d08-0c7d64c49cff",
"name": "\ud83e\udd16 GPT-4o \u2014 Extract Structured Invoice Fields",
"type": "@n8n/n8n-nodes-langchain.openAi",
"notes": "Sends OCR text to GPT-4o with a strict JSON schema prompt. Temperature=0 for deterministic extraction. Returns structured invoice data.",
"position": [
-400,
832
],
"parameters": {
"modelId": {
"__rl": true,
"mode": "list",
"value": "gpt-4o-mini",
"cachedResultName": "GPT-4O-MINI"
},
"options": {
"temperature": 0
},
"messages": {
"values": [
{
"content": "=Validate this invoice and return JSON in exactly this structure:\n\nINPUT INVOICE:\n{{ JSON.stringify($json) }}\n\nRETURN THIS EXACT JSON STRUCTURE:\n{\n \"invoice_number\": \"value\",\n \"invoice_date\": \"value\",\n \"due_date\": \"value\",\n \"vendor_name\": \"value\",\n \"vendor_gstin\": \"value\",\n \"bill_to\": \"value\",\n \"subtotal\": number,\n \"tax_amount\": number,\n \"total_amount\": number,\n \"currency\": \"value\",\n \"line_items_count\": number,\n \"line_items_total\": number,\n \"payment_terms\": \"value or null\",\n \"po_number\": \"value or null\",\n \"status\": \"APPROVED\" or \"NEEDS_REVIEW\",\n \"flags\": [\"array of issue strings, empty if none\"],\n \"summary\": \"one sentence plain English summary of this invoice\"\n}\n\nRules for status:\n- APPROVED if all validations pass\n- NEEDS_REVIEW if any flags exist"
},
{
"role": "system",
"content": "You are an invoice validation and summarization assistant for a finance team.\n\nYou receive structured invoice JSON data and must:\n1. Validate all fields for completeness and correctness\n2. Flag any issues or anomalies\n3. Return a clean validation report in JSON\n\nValidation rules:\n- invoice_number must be present\n- invoice_date and due_date must be valid dates\n- due_date must be after invoice_date\n- total_amount must equal subtotal + tax_amount\n- vendor_gstin must match Indian GST format: 2 digits + 5 letters + 4 digits + 1 letter + 1 alphanumeric + Z + 1 alphanumeric\n- line_items amounts must add up to subtotal\n- flag null fields as warnings\n\nAlways return ONLY valid JSON. No markdown, no explanation."
}
]
}
},
"credentials": {
"openAiApi": {
"name": "<your credential>"
}
},
"typeVersion": 1.3
},
{
"id": "948dd4e4-7083-4382-9b7c-2afab788e521",
"name": "\u2705 Parse & Validate Invoice Data",
"type": "n8n-nodes-base.code",
"notes": "Parses GPT-4o JSON output. Validates: missing fields, high-value threshold (>1L INR), date sanity, math consistency, GSTIN format. Tags status as AUTO_APPROVED or NEEDS_REVIEW.",
"position": [
32,
832
],
"parameters": {
"jsCode": "// Parse GPT-4o JSON output safely\nconst raw = $input.item.json.text || $input.item.json.message?.content || '';\n\nlet parsed;\ntry {\n // Strip any accidental markdown fences\n const cleaned = raw.replace(/```json/g, '').replace(/```/g, '').trim();\n parsed = JSON.parse(cleaned);\n} catch (e) {\n return [{ json: { parse_error: true, raw_text: raw, error: e.message } }];\n}\n\n// --- VALIDATION LOGIC ---\nconst flags = [];\nconst now = new Date();\n\n// 1. Missing critical fields\nif (!parsed.invoice_number) flags.push('MISSING_INVOICE_NUMBER');\nif (!parsed.vendor?.name) flags.push('MISSING_VENDOR_NAME');\nif (!parsed.total_amount || parsed.total_amount === 0) flags.push('MISSING_OR_ZERO_TOTAL');\nif (!parsed.invoice_date) flags.push('MISSING_INVOICE_DATE');\n\n// 2. Amount threshold check (flag if > 1,00,000 INR for extra approval)\nif (parsed.total_amount > 100000) flags.push('HIGH_VALUE_INVOICE');\n\n// 3. Date sanity check\nif (parsed.invoice_date) {\n const invDate = new Date(parsed.invoice_date);\n const monthsAgo = (now - invDate) / (1000 * 60 * 60 * 24 * 30);\n if (monthsAgo > 6) flags.push('STALE_INVOICE_OVER_6_MONTHS');\n if (invDate > now) flags.push('FUTURE_DATED_INVOICE');\n}\n\n// 4. Due date check\nif (parsed.due_date) {\n const due = new Date(parsed.due_date);\n if (due < now) flags.push('OVERDUE_INVOICE');\n}\n\n// 5. Math validation \u2014 subtotal + tax should ~= total\nif (parsed.subtotal && parsed.tax_amount && parsed.total_amount) {\n const expected = parsed.subtotal + parsed.tax_amount - (parsed.discount || 0);\n const diff = Math.abs(expected - parsed.total_amount);\n if (diff > 1) flags.push(`AMOUNT_MISMATCH_DIFF_${diff.toFixed(2)}`);\n}\n\n// 6. GSTIN format check (Indian GST: 15 alphanumeric)\nif (parsed.vendor?.gstin) {\n const gstinRegex = /^[0-9]{2}[A-Z]{5}[0-9]{4}[A-Z]{1}[1-9A-Z]{1}Z[0-9A-Z]{1}$/;\n if (!gstinRegex.test(parsed.vendor.gstin)) flags.push('INVALID_GSTIN_FORMAT');\n}\n\n// Determine approval route\nconst needsHumanReview = flags.length > 0;\nconst status = needsHumanReview ? 'NEEDS_REVIEW' : 'AUTO_APPROVED';\n\nreturn [{\n json: {\n ...parsed,\n _meta: {\n status,\n flags,\n processed_at: new Date().toISOString(),\n source_email_subject: $('Gmail \u2014 Watch Invoice Emails').item.json.subject || '',\n source_email_from: $('Gmail \u2014 Watch Invoice Emails').item.json.from || ''\n }\n }\n}];\n"
},
"typeVersion": 2
},
{
"id": "10db344b-eaf4-4094-8277-daf37d42c470",
"name": "\u2753 Auto-Approved or Needs Review?",
"type": "n8n-nodes-base.if",
"notes": "Routes clean invoices to auto-processing. Flagged invoices go to Slack approval thread.",
"position": [
432,
832
],
"parameters": {
"options": {},
"conditions": {
"options": {
"version": 1,
"leftValue": "",
"caseSensitive": true,
"typeValidation": "strict"
},
"combinator": "and",
"conditions": [
{
"id": "cond-002",
"operator": {
"type": "string",
"operation": "equals"
},
"leftValue": "={{ $json._meta.status }}",
"rightValue": "AUTO_APPROVED"
}
]
}
},
"typeVersion": 2
},
{
"id": "8f2571a8-2570-408a-add8-a11785103d08",
"name": "\ud83d\udcca Google Sheets \u2014 Log Approved Invoice",
"type": "n8n-nodes-base.googleSheets",
"notes": "Appends invoice to master Google Sheet tracker. All 16 fields including status and flags. Used as the single source of truth for finance team.",
"position": [
672,
736
],
"parameters": {
"columns": {
"value": {},
"schema": [],
"mappingMode": "autoMapInputData",
"matchingColumns": [],
"attemptToConvertTypes": false,
"convertFieldsToString": false
},
"options": {},
"operation": "appendOrUpdate",
"sheetName": {
"__rl": true,
"mode": "list",
"value": 1463078804,
"cachedResultUrl": "https://docs.google.com/spreadsheets/d/1fiSPjKE-ELzgTJdNyfE1t8z5_Z7JeE6bBUUTcCjkBH0/edit#gid=1463078804",
"cachedResultName": "Sheet4"
},
"documentId": {
"__rl": true,
"mode": "list",
"value": "1fiSPjKE-ELzgTJdNyfE1t8z5_Z7JeE6bBUUTcCjkBH0",
"cachedResultUrl": "https://docs.google.com/spreadsheets/d/1fiSPjKE-ELzgTJdNyfE1t8z5_Z7JeE6bBUUTcCjkBH0/edit?usp=drivesdk",
"cachedResultName": "IT Allocation"
}
},
"credentials": {
"googleSheetsOAuth2Api": {
"name": "<your credential>"
}
},
"typeVersion": 4.4
},
{
"id": "1aecc27c-2a5a-4bec-adfe-b9807395f52c",
"name": "\ud83d\udd14 Slack \u2014 Notify: Invoice Auto-Approved",
"type": "n8n-nodes-base.slack",
"notes": "Posts clean approval summary to #finance-invoices. No action needed from finance team.",
"position": [
912,
688
],
"parameters": {
"text": "=\u2705 *Invoice Auto-Approved*\n\n*Vendor:* {{ $json.vendor?.name }}\n*Invoice #:* {{ $json.invoice_number }}\n*Date:* {{ $json.invoice_date }}\n*Due:* {{ $json.due_date || 'Not specified' }}\n*Amount:* {{ $json.currency || 'INR' }} {{ $json.total_amount?.toLocaleString('en-IN') }}\n*GSTIN:* {{ $json.vendor?.gstin || 'N/A' }}\n\n_Auto-logged to Google Sheets \u2713_",
"select": "channel",
"channelId": {
"__rl": true,
"mode": "list",
"value": "C0B0FH02CH2",
"cachedResultName": "all-anuj"
},
"otherOptions": {}
},
"credentials": {
"slackApi": {
"name": "<your credential>"
}
},
"typeVersion": 2.3
},
{
"id": "2eeb896c-e40a-4dd8-bdff-29d008a2c44e",
"name": "\ud83d\udea9 Slack \u2014 Flag Invoice for Human Review",
"type": "n8n-nodes-base.slack",
"notes": "Posts flagged invoice to #finance-approvals with all flags listed. Human must react with \u2705 or \u274c emoji to approve/reject.",
"position": [
640,
1088
],
"parameters": {
"text": "=\u26a0\ufe0f *Invoice Needs Human Review*\n\n*From:* {{ $json._meta.source_email_from }}\n*Vendor:* {{ $json.vendor?.name || 'UNKNOWN' }}\n*Invoice #:* {{ $json.invoice_number || 'NOT FOUND' }}\n*Amount:* {{ $json.currency || 'INR' }} {{ $json.total_amount || 0 }}\n*Date:* {{ $json.invoice_date || 'NOT FOUND' }}\n\n*\ud83d\udea9 Flags Raised:*\n{{ $json._meta.flags?.map(f => '\u2022 ' + f).join('\\n') }}\n\n*Action Required:*\n\ud83d\udc4d React with \u2705 to approve and log to Sheets\n\ud83d\udc4e React with \u274c to reject and notify sender\n\n_Processed at {{ $json._meta.processed_at }}_",
"select": "channel",
"channelId": {
"__rl": true,
"mode": "list",
"value": "C0B0FH02CH2",
"cachedResultName": "all-anuj"
},
"otherOptions": {}
},
"credentials": {
"slackApi": {
"name": "<your credential>"
}
},
"typeVersion": 2.3
},
{
"id": "ebc0aa11-3956-4a70-8fad-a67eb4978d73",
"name": "\ud83d\udccb Google Sheets \u2014 Log Flagged Invoice",
"type": "n8n-nodes-base.googleSheets",
"notes": "Also logs flagged invoices to Sheets with NEEDS_REVIEW status so nothing is lost.",
"position": [
912,
976
],
"parameters": {
"columns": {
"value": {},
"schema": [
{
"id": "invoice_number",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "invoice_number",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "invoice_date",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "invoice_date",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "due_date",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "due_date",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "vendor_name",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "vendor_name",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "vendor_gstin",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "vendor_gstin",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "bill_to",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "bill_to",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "subtotal",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "subtotal",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "tax_amount",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "tax_amount",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "total_amount",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "total_amount",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "currency",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "currency",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "line_items_count",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "line_items_count",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "line_items_total",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "line_items_total",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "payment_terms",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "payment_terms",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "po_number",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "po_number",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "status",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "status",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "flags",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "flags",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "summary",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "summary",
"defaultMatch": false,
"canBeUsedToMatch": true
},
{
"id": "_meta",
"type": "string",
"display": true,
"removed": false,
"required": false,
"displayName": "_meta",
"defaultMatch": false,
"canBeUsedToMatch": true
}
],
"mappingMode": "autoMapInputData",
"matchingColumns": [],
"attemptToConvertTypes": false,
"convertFieldsToString": false
},
"options": {},
"operation": "appendOrUpdate",
"sheetName": {
"__rl": true,
"mode": "list",
"value": 1463078804,
"cachedResultUrl": "https://docs.google.com/spreadsheets/d/1fiSPjKE-ELzgTJdNyfE1t8z5_Z7JeE6bBUUTcCjkBH0/edit#gid=1463078804",
"cachedResultName": "Sheet4"
},
"documentId": {
"__rl": true,
"mode": "list",
"value": "1fiSPjKE-ELzgTJdNyfE1t8z5_Z7JeE6bBUUTcCjkBH0",
"cachedResultUrl": "https://docs.google.com/spreadsheets/d/1fiSPjKE-ELzgTJdNyfE1t8z5_Z7JeE6bBUUTcCjkBH0/edit?usp=drivesdk",
"cachedResultName": "IT Allocation"
}
},
"credentials": {
"googleSheetsOAuth2Api": {
"name": "<your credential>"
}
},
"typeVersion": 4.4
},
{
"id": "2a25b1ec-279f-455b-8b75-598c1b21e849",
"name": "\ud83d\udea8 Slack \u2014 Alert: No Attachment Found",
"type": "n8n-nodes-base.slack",
"notes": "Notifies finance team when an invoice email arrives with no attachment so nothing slips through.",
"position": [
-1584,
1056
],
"parameters": {
"text": "=\u2139\ufe0f Invoice email received from {{ $json.from }} but *no PDF attachment found*.\n\nSubject: {{ $json.subject }}\n\nPlease forward with attachment attached.",
"select": "channel",
"channelId": {
"__rl": true,
"mode": "list",
"value": "C0B0FH02CH2",
"cachedResultName": "all-anuj"
},
"otherOptions": {}
},
"credentials": {
"slackApi": {
"name": "<your credential>"
}
},
"typeVersion": 2.3
},
{
"id": "4bab0786-8e32-4edf-bea8-4951d69de20e",
"name": "\ud83d\udd27 Prepare Email Metadata",
"type": "n8n-nodes-base.code",
"position": [
-2016,
896
],
"parameters": {
"jsCode": "// Code node (JavaScript) \u2014 paste into \"Run Once for Each Item\"\nconst headers = $input.item.json.headers || {};\n\n// Signal 1: Outlook \"has attachment\" header\nconst outlookFlag = (headers[\"x-ms-has-attach\"] || \"\")\n .toLowerCase().includes(\"yes\");\n\n// Signal 2: MIME multipart/mixed (universal)\nconst mimeFlag = (headers[\"content-type\"] || \"\")\n .toLowerCase().includes(\"multipart/mixed\");\n\n// Signal 3: sizeEstimate > 50KB suggests binary attachment\nconst sizeFlag = ($input.item.json.sizeEstimate || 0) > 50000;\n\nconst hasAttachment = outlookFlag || mimeFlag;\n\nreturn [{\n json: {\n ...$input.item.json, // pass all original fields through\n has_attachment: hasAttachment,\n attachment_signals: {\n outlook_header: outlookFlag,\n mime_multipart: mimeFlag,\n large_size: sizeFlag\n }\n }\n}];"
},
"typeVersion": 2
},
{
"id": "399bf4f1-3aa9-4964-913e-ed1e927fafce",
"name": "\ud83c\udf10 Mistral OCR \u2014 Parse Invoice Image",
"type": "n8n-nodes-base.httpRequest",
"position": [
-944,
832
],
"parameters": {
"url": "https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:generateContent?key=YOUR_TOKEN_HERE",
"method": "POST",
"options": {},
"jsonBody": "={\n \"contents\": [{\n \"parts\": [\n {\n \"inline_data\": {\n \"mime_type\": \"application/pdf\",\n \"data\": \"{{ $json.data }}\"\n }\n },\n {\n \"text\": \"Extract all invoice fields and return ONLY valid JSON: invoice_number, invoice_date, due_date, vendor_name, vendor_gstin, bill_to, subtotal, tax_amount, total_amount, currency, line_items, payment_terms, po_number. Use null for missing fields. No markdown, no explanation.\"\n }\n ]\n }]\n}",
"sendBody": true,
"sendHeaders": true,
"specifyBody": "json",
"headerParameters": {
"parameters": [
{
"name": "x-goog-api-key",
"value": "AIzaYOUR_GOOGLE_API_KEY_HERE"
}
]
}
},
"typeVersion": 4.4
},
{
"id": "edf56afe-4c96-4424-b30d-1ee18100e2c2",
"name": "\ud83d\udcc4 Extract Raw File Content",
"type": "n8n-nodes-base.extractFromFile",
"position": [
-1392,
832
],
"parameters": {
"options": {},
"operation": "binaryToPropery",
"binaryPropertyName": "attachment_0"
},
"typeVersion": 1.1
},
{
"id": "434dbf05-9b9e-4584-a0e5-98f5bc344e5f",
"name": "\ud83d\udd0d Extract Text from PDF",
"type": "n8n-nodes-base.extractFromFile",
"position": [
-1168,
832
],
"parameters": {
"options": {},
"operation": "binaryToPropery",
"binaryPropertyName": "attachment_1"
},
"typeVersion": 1.1
},
{
"id": "2da5361f-df34-489b-9141-bdd62c1b821f",
"name": "\ud83e\uddf9 Clean & Normalise OCR Output",
"type": "n8n-nodes-base.code",
"position": [
-672,
832
],
"parameters": {
"jsCode": "// Extract the text from Gemini's response structure\nconst raw = $input.item.json.candidates[0].content.parts[0].text;\n\n// Parse the JSON string\nconst invoice = JSON.parse(raw);\n\nreturn [{ json: invoice }];"
},
"typeVersion": 2
},
{
"id": "39838335-cb59-426d-94de-15da23320845",
"name": "Sticky Note \u2014 Phase 1: Email Intake & Attachment Check",
"type": "n8n-nodes-base.stickyNote",
"position": [
-2336,
640
],
"parameters": {
"color": 3,
"width": 500,
"height": 217,
"content": "## \ud83d\udce5 Phase 1: Email Intake & Attachment Check\nWatches Gmail for incoming invoice emails.\nPrepares email metadata, then checks whether a PDF attachment is present:\n- \u2705 **Has attachment** \u2192 download and proceed to OCR pipeline\n- \u274c **No attachment** \u2192 immediately alert the team via Slack and stop"
},
"typeVersion": 1
},
{
"id": "5bc90691-6209-418a-a9d3-127de33fbf6d",
"name": "Sticky Note \u2014 Phase 2: OCR Extraction Pipeline",
"type": "n8n-nodes-base.stickyNote",
"position": [
-1456,
544
],
"parameters": {
"color": 5,
"width": 510,
"height": 232,
"content": "## \ud83d\udd0d Phase 2: OCR Extraction Pipeline\nProcesses the downloaded invoice PDF through a multi-stage OCR pipeline:\n1. **Extract raw file content** from the attachment\n2. **Extract text layer** from the PDF\n3. **Mistral OCR** parses the invoice as an image for scanned/non-text PDFs\n4. **Clean & normalise** the raw OCR output for consistent formatting before AI processing"
},
"typeVersion": 1
},
{
"id": "2a9277e2-4001-492f-aa95-338ef4958dbf",
"name": "Sticky Note \u2014 Phase 3: GPT-4o Structured Field Extraction",
"type": "n8n-nodes-base.stickyNote",
"position": [
-672,
544
],
"parameters": {
"color": 4,
"width": 530,
"height": 263,
"content": "## \ud83e\udd16 Phase 3: GPT-4o \u2014 Structured Field Extraction\n**GPT-4o** reads the cleaned OCR text and extracts structured invoice fields:\n- Vendor name, invoice number, date, due date\n- Line items, quantities, unit prices\n- Subtotal, tax, total amount, currency\n\nOutput is then **parsed and validated** by a code node to enforce data types, flag missing fields, and apply business rules (e.g. amount thresholds for auto-approval)."
},
"typeVersion": 1
},
{
"id": "8be3c0cd-ba09-46c4-8d85-e0358b1a22a0",
"name": "Sticky Note \u2014 Phase 4: Auto-Approval Routing",
"type": "n8n-nodes-base.stickyNote",
"position": [
208,
528
],
"parameters": {
"color": 6,
"width": 490,
"height": 207,
"content": "## \u2705 Phase 4: Auto-Approval or Human Review Routing\nRoutes each invoice based on validation outcome and business rules:\n- \u2705 **Auto-Approved** \u2192 log to Google Sheets + Slack notification to finance team\n- \ud83d\udea9 **Needs Review** \u2192 log as flagged in Google Sheets + Slack alert to reviewer with reason"
},
"typeVersion": 1
},
{
"id": "e24bcce1-fb5f-4bb3-9046-8af4a2f7038a",
"name": "Sticky Note \u2014 Phase 5: Logging & Notifications",
"type": "n8n-nodes-base.stickyNote",
"position": [
1152,
592
],
"parameters": {
"color": 7,
"width": 460,
"height": 265,
"content": "## \ud83d\udcca Phase 5: Logging & Team Notifications\n**Auto-Approved path:**\n- Google Sheets logs the invoice with status **Approved**\n- Slack notifies the finance team with invoice summary\n\n**Flagged path:**\n- Google Sheets logs the invoice with status **Flagged for Review**\n- Slack alerts the reviewer with the specific flag reason for manual action"
},
"typeVersion": 1
},
{
"id": "fe4ece6f-8d2b-41e5-bb25-e3c7de32be48",
"name": "Sticky Note \u2014 Error Path: No Attachment",
"type": "n8n-nodes-base.stickyNote",
"position": [
-1360,
1104
],
"parameters": {
"color": 2,
"width": 420,
"height": 151,
"content": "## \ud83d\udea8 Error Path: No Attachment Found\nIf the incoming email has no PDF attachment, the workflow exits early and sends a **Slack alert** with the sender and subject so the team can follow up directly."
},
"typeVersion": 1
}
],
"active": false,
"settings": {
"binaryMode": "separate",
"executionOrder": "v1"
},
"versionId": "64f87a32-931f-41a7-aa45-b56796f55162",
"connections": {
"\u2753 Has PDF Attachment?": {
"main": [
[
{
"node": "\ud83d\udcce Gmail \u2014 Download Invoice Attachment",
"type": "main",
"index": 0
}
],
[
{
"node": "\ud83d\udea8 Slack \u2014 Alert: No Attachment Found",
"type": "main",
"index": 0
}
]
]
},
"\ud83d\udd0d Extract Text from PDF": {
"main": [
[
{
"node": "\ud83c\udf10 Mistral OCR \u2014 Parse Invoice Image",
"type": "main",
"index": 0
}
]
]
},
"\ud83d\udd27 Prepare Email Metadata": {
"main": [
[
{
"node": "\u2753 Has PDF Attachment?",
"type": "main",
"index": 0
}
]
]
},
"\ud83d\udcc4 Extract Raw File Content": {
"main": [
[
{
"node": "\ud83d\udd0d Extract Text from PDF",
"type": "main",
"index": 0
}
]
]
},
"\u2705 Parse & Validate Invoice Data": {
"main": [
[
{
"node": "\u2753 Auto-Approved or Needs Review?",
"type": "main",
"index": 0
}
]
]
},
"\ud83e\uddf9 Clean & Normalise OCR Output": {
"main": [
[
{
"node": "\ud83e\udd16 GPT-4o \u2014 Extract Structured Invoice Fields",
"type": "main",
"index": 0
}
]
]
},
"\u2753 Auto-Approved or Needs Review?": {
"main": [
[
{
"node": "\ud83d\udcca Google Sheets \u2014 Log Approved Invoice",
"type": "main",
"index": 0
}
],
[
{
"node": "\ud83d\udea9 Slack \u2014 Flag Invoice for Human Review",
"type": "main",
"index": 0
},
{
"node": "\ud83d\udccb Google Sheets \u2014 Log Flagged Invoice",
"type": "main",
"index": 0
}
]
]
},
"\ud83d\udce7 Gmail \u2014 Watch for Invoice Emails": {
"main": [
[
{
"node": "\ud83d\udd27 Prepare Email Metadata",
"type": "main",
"index": 0
}
]
]
},
"\ud83c\udf10 Mistral OCR \u2014 Parse Invoice Image": {
"main": [
[
{
"node": "\ud83e\uddf9 Clean & Normalise OCR Output",
"type": "main",
"index": 0
}
]
]
},
"\ud83d\udcce Gmail \u2014 Download Invoice Attachment": {
"main": [
[
{
"node": "\ud83d\udcc4 Extract Raw File Content",
"type": "main",
"index": 0
}
]
]
},
"\ud83d\udcca Google Sheets \u2014 Log Approved Invoice": {
"main": [
[
{
"node": "\ud83d\udd14 Slack \u2014 Notify: Invoice Auto-Approved",
"type": "main",
"index": 0
}
]
]
},
"\ud83e\udd16 GPT-4o \u2014 Extract Structured Invoice Fields": {
"main": [
[
{
"node": "\u2705 Parse & Validate Invoice Data",
"type": "main",
"index": 0
}
]
]
}
}
}
Credentials you'll need
Each integration node will prompt for credentials when you import. We strip credential IDs before publishing — you'll add your own.
gmailOAuth2googleSheetsOAuth2ApiopenAiApislackApi
Pro
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About this workflow
Automate your entire invoice processing pipeline with AI-powered OCR, validation, and approval workflows 📄🤖. This n8n automation monitors incoming Gmail invoices, extracts structured data using OCR and GPT-4o, validates invoice accuracy, and automatically routes clean invoices…
Source: https://n8n.io/workflows/15694/ — original creator credit. Request a take-down →
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