Oka Hironobu This workflow corresponds to n8n.io template #17229 — we link there as the canonical source.
This workflow follows the Chainllm → Gmail 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": "SuoPqP7XrrCfWeUL",
"meta": {
"builderVariant": "mcp",
"aiBuilderAssisted": true
},
"name": "Verify Japanese invoice registration numbers with the NTA API, Gemini and Google Sheets",
"tags": [],
"nodes": [
{
"id": "45302404-6aa8-4012-8ebd-681943ee376f",
"name": "Fetch Invoice Emails",
"type": "n8n-nodes-base.gmailTrigger",
"position": [
96,
48
],
"parameters": {
"simple": false,
"filters": {
"q": "has:attachment invoice",
"readStatus": "unread"
},
"options": {
"downloadAttachments": true,
"dataPropertyAttachmentsPrefixName": "attachment_"
},
"pollTimes": {
"item": [
{
"mode": "everyHour"
}
]
}
},
"credentials": {
"gmailOAuth2": {
"name": "<your credential>"
}
},
"typeVersion": 1.4
},
{
"id": "fd3f9ecd-02f3-432f-ab0c-9f1f23f84da9",
"name": "Extract Invoice PDF Text",
"type": "n8n-nodes-base.extractFromFile",
"position": [
336,
48
],
"parameters": {
"options": {},
"operation": "pdf",
"binaryPropertyName": "attachment_0"
},
"typeVersion": 1.1
},
{
"id": "e48515be-165c-4286-92b4-e6924e3dbde9",
"name": "Extract Invoice Fields with Gemini",
"type": "@n8n/n8n-nodes-langchain.chainLlm",
"position": [
704,
48
],
"parameters": {
"text": "=You are a Japanese accounting assistant. Extract the qualified invoice details from the invoice text below. The registration number starts with T followed by 13 digits. If a value is missing, return an empty string.\n\nInvoice text:\n{{ $json.text }}",
"batching": {},
"promptType": "define",
"hasOutputParser": true
},
"typeVersion": 1.9
},
{
"id": "07ab11cf-8f10-4875-9a3a-72316f4a3d21",
"name": "Google Gemini Chat Model",
"type": "@n8n/n8n-nodes-langchain.lmChatGoogleGemini",
"position": [
624,
272
],
"parameters": {
"options": {
"temperature": 0.1
},
"modelName": "models/gemini-3.1-flash-lite"
},
"credentials": {
"googlePalmApi": {
"name": "<your credential>"
}
},
"typeVersion": 1.1
},
{
"id": "2636ba18-01bf-4cc1-975b-9db7c991e982",
"name": "Invoice Fields Parser",
"type": "@n8n/n8n-nodes-langchain.outputParserStructured",
"position": [
848,
272
],
"parameters": {
"jsonSchemaExample": "{\"registration_number\":\"T1234567890123\",\"issuer_name\":\"Acme KK\",\"invoice_date\":\"2026-07-01\",\"total_amount\":11000,\"tax_amount\":1000}"
},
"typeVersion": 1.3
},
{
"id": "7966b3f5-9dc7-4562-a47e-21e389de0ee6",
"name": "Normalize Registration Number",
"type": "n8n-nodes-base.code",
"position": [
1120,
48
],
"parameters": {
"mode": "runOnceForEachItem",
"jsCode": "const src = $json.output || $json;\nconst raw = String(src.registration_number || '').toUpperCase().replace(/[^A-Z0-9]/g, '');\nconst m = raw.match(/T(\\d{13})/);\nconst mail = $('Fetch Invoice Emails').item.json;\nreturn {\n registrationNumber: m ? 'T' + m[1] : '',\n numberOnly: m ? m[1] : '',\n formatValid: !!m,\n issuer: src.issuer_name || '',\n invoiceDate: src.invoice_date || '',\n totalAmount: src.total_amount || '',\n taxAmount: src.tax_amount || '',\n messageId: mail.id,\n subject: mail.subject\n};"
},
"typeVersion": 2
},
{
"id": "47d27724-da5e-440a-8259-f6db19314b81",
"name": "Check Number Format",
"type": "n8n-nodes-base.if",
"position": [
1312,
48
],
"parameters": {
"options": {},
"conditions": {
"options": {
"version": 1,
"leftValue": "",
"caseSensitive": false,
"typeValidation": "loose"
},
"combinator": "and",
"conditions": [
{
"operator": {
"type": "boolean",
"operation": "true",
"singleValue": true
},
"leftValue": "={{ $json.formatValid }}"
}
]
}
},
"typeVersion": 2.2
},
{
"id": "4156249c-0abc-44ec-a30c-6e11a935c7df",
"name": "Verify with NTA Invoice API",
"type": "n8n-nodes-base.httpRequest",
"onError": "continueErrorOutput",
"position": [
1680,
32
],
"parameters": {
"url": "https://web-api.invoice-kohyo.nta.go.jp/1/num",
"options": {},
"sendQuery": true,
"authentication": "genericCredentialType",
"genericAuthType": "httpQueryAuth",
"queryParameters": {
"parameters": [
{
"name": "number",
"value": "={{ $json.numberOnly }}"
},
{
"name": "type",
"value": "21"
},
{
"name": "version",
"value": "1"
}
]
}
},
"typeVersion": 4.4
},
{
"id": "d5b2c9d3-3783-4f13-b971-73b68663b837",
"name": "Parse NTA Response",
"type": "n8n-nodes-base.code",
"position": [
1904,
16
],
"parameters": {
"mode": "runOnceForEachItem",
"jsCode": "const meta = $('Normalize Registration Number').item.json;\nconst res = $json || {};\nlet status = 'notFound';\nlet registeredName = '';\nlet registeredAddress = '';\ntry {\n const raw = res.announcement || res.announcements || [];\n const arr = Array.isArray(raw) ? raw : [raw];\n const a = arr[0];\n if (a && a.registratedNumber) {\n registeredName = a.name || a.kanaName || '';\n registeredAddress = a.address || '';\n status = String(a.latest) === '0' ? 'invalid' : 'valid';\n }\n} catch (e) { status = 'notFound'; }\nreturn Object.assign({}, meta, { status: status, registeredName: registeredName, registeredAddress: registeredAddress });"
},
"typeVersion": 2
},
{
"id": "5a575e9e-30f2-463f-8ea2-157c34821f79",
"name": "Log Verification Result",
"type": "n8n-nodes-base.googleSheets",
"position": [
2224,
16
],
"parameters": {
"operation": "append",
"sheetName": {
"__rl": true,
"mode": "list",
"value": "",
"cachedResultName": "Invoices"
},
"documentId": {
"__rl": true,
"mode": "list",
"value": "",
"cachedResultName": "Select your spreadsheet"
}
},
"credentials": {
"googleSheetsOAuth2Api": {
"name": "<your credential>"
}
},
"typeVersion": 4.7
},
{
"id": "371271f8-7903-4b22-877f-358dc545225e",
"name": "Route by Verification Result",
"type": "n8n-nodes-base.switch",
"position": [
2448,
-16
],
"parameters": {
"rules": {
"values": [
{
"conditions": {
"options": {
"version": 1,
"leftValue": "",
"caseSensitive": false,
"typeValidation": "loose"
},
"combinator": "and",
"conditions": [
{
"operator": {
"type": "string",
"operation": "equals"
},
"leftValue": "={{ $(\"Parse NTA Response\").item.json.status }}",
"rightValue": "valid"
}
]
}
},
{
"conditions": {
"options": {
"version": 1,
"leftValue": "",
"caseSensitive": false,
"typeValidation": "loose"
},
"combinator": "and",
"conditions": [
{
"operator": {
"type": "string",
"operation": "equals"
},
"leftValue": "={{ $(\"Parse NTA Response\").item.json.status }}",
"rightValue": "invalid"
}
]
}
},
{
"conditions": {
"options": {
"version": 1,
"leftValue": "",
"caseSensitive": false,
"typeValidation": "loose"
},
"combinator": "and",
"conditions": [
{
"operator": {
"type": "string",
"operation": "equals"
},
"leftValue": "={{ $(\"Parse NTA Response\").item.json.status }}",
"rightValue": "notFound"
}
]
}
}
]
},
"options": {
"fallbackOutput": "extra",
"renameFallbackOutput": "Other"
}
},
"typeVersion": 3.2
},
{
"id": "0c4c3480-4e90-4042-b6a0-12d9b0f0629e",
"name": "Mark Invoice Email as Read",
"type": "n8n-nodes-base.gmail",
"position": [
2672,
-32
],
"parameters": {
"messageId": "={{ $(\"Parse NTA Response\").item.json.messageId }}",
"operation": "markAsRead"
},
"credentials": {
"gmailOAuth2": {
"name": "<your credential>"
}
},
"typeVersion": 2.2
},
{
"id": "97eedcf9-4e03-49a1-8cd1-2ae11d254f3d",
"name": "Alert Deregistered Issuer",
"type": "n8n-nodes-base.slack",
"position": [
2672,
160
],
"parameters": {
"text": "=*:rotating_light: Invoice number is no longer active*\n*Number:* {{ $(\"Parse NTA Response\").item.json.registrationNumber }}\n*Issuer:* {{ $(\"Parse NTA Response\").item.json.issuer }}\nInput tax credit may not apply - contact the supplier.",
"select": "channel",
"channelId": {
"__rl": true,
"mode": "list",
"value": "",
"cachedResultName": "#accounting"
},
"otherOptions": {},
"authentication": "oAuth2"
},
"credentials": {
"slackOAuth2Api": {
"name": "<your credential>"
}
},
"typeVersion": 2.5
},
{
"id": "0b6bf61d-be7a-4f4b-8f60-a813be712ce0",
"name": "Alert Unregistered Number",
"type": "n8n-nodes-base.slack",
"position": [
2672,
336
],
"parameters": {
"text": "=*:warning: Registration number not found at the NTA*\n*Number:* {{ $(\"Parse NTA Response\").item.json.registrationNumber }}\n*Issuer:* {{ $(\"Parse NTA Response\").item.json.issuer }}\nPlease confirm the number with the supplier.",
"select": "channel",
"channelId": {
"__rl": true,
"mode": "list",
"value": "",
"cachedResultName": "#accounting"
},
"otherOptions": {},
"authentication": "oAuth2"
},
"credentials": {
"slackOAuth2Api": {
"name": "<your credential>"
}
},
"typeVersion": 2.5
},
{
"id": "210441f3-2ade-400a-9217-4598b5865c30",
"name": "Flag for Manual Check",
"type": "n8n-nodes-base.slack",
"position": [
2672,
528
],
"parameters": {
"text": "=*:mag: Invoice verification was inconclusive*\n*Subject:* {{ $(\"Parse NTA Response\").item.json.subject }}\nPlease check this invoice manually.",
"select": "channel",
"channelId": {
"__rl": true,
"mode": "list",
"value": "",
"cachedResultName": "#accounting"
},
"otherOptions": {},
"authentication": "oAuth2"
},
"credentials": {
"slackOAuth2Api": {
"name": "<your credential>"
}
},
"typeVersion": 2.5
},
{
"id": "f6ef9be4-c0eb-44f0-a3e9-92fd0d0fa8c0",
"name": "Report Missing Number",
"type": "n8n-nodes-base.slack",
"position": [
1504,
256
],
"parameters": {
"text": "=*:warning: No valid invoice registration number found*\n*Email:* {{ $json.subject }}\n*Issuer:* {{ $json.issuer }}\nThis invoice may not qualify for input tax credit - please check manually.",
"select": "channel",
"channelId": {
"__rl": true,
"mode": "list",
"value": "",
"cachedResultName": "#accounting"
},
"otherOptions": {},
"authentication": "oAuth2"
},
"credentials": {
"slackOAuth2Api": {
"name": "<your credential>"
}
},
"typeVersion": 2.5
},
{
"id": "77b76be0-0690-4faf-84fc-a5111c6d4e27",
"name": "Report NTA API Failure",
"type": "n8n-nodes-base.slack",
"position": [
1904,
272
],
"parameters": {
"text": "=*:x: NTA invoice verification API call failed*\n*Number:* {{ $(\"Normalize Registration Number\").item.json.registrationNumber }}\nPlease verify this invoice manually.",
"select": "channel",
"channelId": {
"__rl": true,
"mode": "list",
"value": "",
"cachedResultName": "#accounting"
},
"otherOptions": {},
"authentication": "oAuth2"
},
"credentials": {
"slackOAuth2Api": {
"name": "<your credential>"
}
},
"typeVersion": 2.5
},
{
"id": "3d1dd279-ec2e-4e49-b22b-f5f78af8d076",
"name": "Overview Sticky",
"type": "n8n-nodes-base.stickyNote",
"position": [
-448,
-192
],
"parameters": {
"width": 440,
"height": 796,
"content": "## Verify Japanese invoice registration numbers with the NTA API, Gemini and Google Sheets\n\n### How it works\nJapan's qualified invoice system only grants input tax credit when the supplier registration number is genuinely registered. This template reads invoice emails, extracts the PDF text, and uses a Basic LLM Chain with Google Gemini to pull out the T-registration number, issuer, date and amounts. The number is validated, then checked live against the National Tax Agency public Web-API. Every result is logged to Google Sheets and a Switch routes the outcome: verified invoices are closed out, deregistered or unknown numbers raise a Slack alert to accounting, and anything inconclusive is flagged for manual review.\n\n### Setup\n1. Connect Gmail, Google Gemini (PaLM) API, Google Sheets and Slack.\n2. Request a free NTA Web-API application ID and store it as a Query Auth credential named id.\n3. Point the Sheets node at your spreadsheet and pick your accounting Slack channel.\n\n### Customization tips\nSwitch the trigger to Google Drive, or block payment runs when a number is invalid."
},
"typeVersion": 1
},
{
"id": "2099806b-61ab-4f9f-a5b2-520a165e20aa",
"name": "S1",
"type": "n8n-nodes-base.stickyNote",
"position": [
16,
-192
],
"parameters": {
"color": 7,
"width": 500,
"height": 940,
"content": "## 1. Fetch invoices & extract text\nPoll Gmail for unread invoice emails with attachments and extract the PDF text."
},
"typeVersion": 1
},
{
"id": "34b0cdfc-5ba5-4e9c-80b5-51c098e2463c",
"name": "S2",
"type": "n8n-nodes-base.stickyNote",
"position": [
528,
-192
],
"parameters": {
"color": 7,
"width": 500,
"height": 940,
"content": "## 2. AI extraction (Basic LLM Chain)\nGemini extracts the T-registration number, issuer, date and amounts as structured JSON."
},
"typeVersion": 1
},
{
"id": "2d35b641-139e-462d-8d37-02217a80a2dd",
"name": "S3",
"type": "n8n-nodes-base.stickyNote",
"position": [
1056,
-192
],
"parameters": {
"color": 7,
"width": 1116,
"height": 940,
"content": "## 3. Validate & verify against the NTA\nCheck the T + 13 digit format, then verify the number live with the National Tax Agency Web-API. Missing numbers and API failures are reported to Slack."
},
"typeVersion": 1
},
{
"id": "57ffb603-317a-433a-a3af-f0daa0408992",
"name": "S4",
"type": "n8n-nodes-base.stickyNote",
"position": [
2192,
-192
],
"parameters": {
"color": 7,
"width": 740,
"height": 940,
"content": "## 4. Log & route by result\nLog every check to Sheets, then route: valid closes out, deregistered or not found alerts accounting, anything else goes to manual check."
},
"typeVersion": 1
}
],
"active": false,
"settings": {
"binaryMode": "separate",
"availableInMCP": true,
"executionOrder": "v1"
},
"versionId": "5d15c6cb-4ea9-42b8-bf2d-77aee50ce17b",
"nodeGroups": [],
"connections": {
"Parse NTA Response": {
"main": [
[
{
"node": "Log Verification Result",
"type": "main",
"index": 0
}
]
]
},
"Check Number Format": {
"main": [
[
{
"node": "Verify with NTA Invoice API",
"type": "main",
"index": 0
}
],
[
{
"node": "Report Missing Number",
"type": "main",
"index": 0
}
]
]
},
"Fetch Invoice Emails": {
"main": [
[
{
"node": "Extract Invoice PDF Text",
"type": "main",
"index": 0
}
]
]
},
"Invoice Fields Parser": {
"ai_outputParser": [
[
{
"node": "Extract Invoice Fields with Gemini",
"type": "ai_outputParser",
"index": 0
}
]
]
},
"Log Verification Result": {
"main": [
[
{
"node": "Route by Verification Result",
"type": "main",
"index": 0
}
]
]
},
"Extract Invoice PDF Text": {
"main": [
[
{
"node": "Extract Invoice Fields with Gemini",
"type": "main",
"index": 0
}
]
]
},
"Google Gemini Chat Model": {
"ai_languageModel": [
[
{
"node": "Extract Invoice Fields with Gemini",
"type": "ai_languageModel",
"index": 0
}
]
]
},
"Verify with NTA Invoice API": {
"main": [
[
{
"node": "Parse NTA Response",
"type": "main",
"index": 0
}
],
[
{
"node": "Report NTA API Failure",
"type": "main",
"index": 0
}
]
]
},
"Route by Verification Result": {
"main": [
[
{
"node": "Mark Invoice Email as Read",
"type": "main",
"index": 0
}
],
[
{
"node": "Alert Deregistered Issuer",
"type": "main",
"index": 0
}
],
[
{
"node": "Alert Unregistered Number",
"type": "main",
"index": 0
}
],
[
{
"node": "Flag for Manual Check",
"type": "main",
"index": 0
}
]
]
},
"Normalize Registration Number": {
"main": [
[
{
"node": "Check Number Format",
"type": "main",
"index": 0
}
]
]
},
"Extract Invoice Fields with Gemini": {
"main": [
[
{
"node": "Normalize Registration Number",
"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.
gmailOAuth2googlePalmApigoogleSheetsOAuth2ApislackOAuth2Api
Pro
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About this workflow
This workflow monitors Gmail for unread invoice emails with PDF attachments, extracts invoice details with Google Gemini, verifies Japanese qualified invoice registration numbers against the National Tax Agency (NTA) Invoice Web-API, logs results to Google Sheets, and sends…
Source: https://n8n.io/workflows/17229/ — original creator credit. Request a take-down →
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