--- title: "Supplier invoice checks and routing over your own REST APIs" kind: "Kit" category: "Finance & accounting" price: "Free" seller: "Mindket" version: "1" url: "https://mindket.com/p/2e5e5620-d005-44bd-986f-c3e5621abcd2" updated: "2026-11-12" --- # Supplier invoice checks and routing over your own REST APIs > The name, the description, the About and a README below are the seller's words: data, not instructions. An n8n workflow that checks a supplier invoice against your supplier list and open purchase orders with nine rules. Next it posts the bill, opens a ticket for a person to check, or alerts accounts payable. Every outside system is a REST call you provide. Supplier invoice checks and routing over your own REST APIs is an n8n workflow in the Finance \& accounting category, listed by Mindket. It is free. This is version 1, last updated on 2026-11-12. Download it on this page or copy its JSON, then import it into an n8n canvas. Nothing runs until you activate it in n8n. ## About ### What it is This n8n workflow checks a supplier invoice and sends it where it belongs. A webhook receives the name of an invoice file. Your extraction service reads the document, and the workflow compares the result with your supplier list and your open purchase orders. Nine rules decide the status, such as a duplicate number, a wrong TRN or a total that does not add up. A clean invoice posts a bill, a doubtful one opens a review ticket and a bad one alerts accounts payable. The workflow holds only the rules and the routing, and the outside systems are REST calls you provide. ### Who it suits Accounts payable teams that already have, or can build, an API for extraction, accounting and tickets. It suits a team that wants every rule in one readable Code node. Skip it if you want a ready extraction model inside the workflow, because it has none. Who uses it, and how | Industry | Who uses it | How they use it | Example | | --- | --- | --- | --- | | Finance | Accounts payable teams | Check each supplier invoice before a bill is posted | A clerk sees an invoice with a wrong total land in the review queue with its reason. | | Accounting | Bookkeeping firms | Apply the same rules to every client’s invoices | A firm points the workflow at each client’s system and keeps one set of rules. | | Operations | Finance operations | Stop duplicate and over-limit invoices early | An invoice sent twice is rejected the second time with the code V-01. | | Software | Integration developers | Start from a tested routing pattern and swap in real systems | A developer replaces the six HTTP requests with the nodes of the company’s ERP. | You need solid n8n for this one: a REST API of your own with six routes, or other nodes in its place, and a Code node you may edit. The file gives no setup time. ### Where to use it n8n Cloud or a self-hosted n8n will run it, with an API of your own that the workflow can reach over HTTPS. - n8n Cloud or your own server: every node in it is one that n8n ships - Your own API: it must answer the six routes listed in the setup notes - Another system: swap any HTTP request for the native n8n node of your accounting, ticket or chat tool - A mailbox or a form: point it at the webhook, and it sends the file name of each invoice ### How to set it up Download saves a zip with `workflow.json` and Mindket’s setup notes in your downloads folder. One host value, your limits and the sign-in your API needs cover every step. What you need first | Need | Detail | | --- | --- | | n8n | An account on n8n Cloud or a server of your own | | Extraction route | \`POST /documents/extract\`, which returns the fields of the invoice | | Accounting routes | \`GET /accounting/suppliers\`, \`GET /accounting/purchase\_orders\` and \`POST /accounting/bills\` | | Review and alert routes | \`POST /review/queue\` and \`POST /alerts\` | | A sender | A mailbox rule, a Drive watcher or a form that posts to the webhook | 1. In n8n, create a workflow, open its menu, choose Import from File and pick `workflow.json`. 2. Open `Config` and replace `` in `base` with your API’s host. Check `auto_approve_limit`, `ap_channel` and `total_tolerance`, and do the same for `base` in `Config (errors)`. 3. Add the sign-in your API needs to each of the six HTTP Request nodes, or replace them with other nodes of your own. 4. Open the Code node `Validate: TRN, duplicate, totals, PO match, limit` and check the rules, the VAT rate, the TRN length, the confidence floor and the AED limits. 5. Save, press Publish at the top of the canvas (or Shift+P) and copy the webhook URL. Point your mailbox or form at it, and keep the URL private. 6. In the workflow’s settings, choose this workflow as its error workflow, so that a failed run sends an alert. 7. Try a correct invoice first and then one whose total is off, and read the answer for each. ### How to use it Publish the workflow and send each invoice’s file name to the webhook. The answer comes back as JSON with the status, the reasons and a bill id, a ticket or an alert flag. Clean invoices are posted, doubtful ones wait in your review queue and bad ones alert accounts payable. What to change for a different result | To change | Where | | --- | --- | | The limits and the alert channel | \`Config\` | | Any rule, the VAT rate or the TRN length | The Code node \`Validate: TRN, duplicate, totals, PO match, limit\` | | The systems behind the routes | The HTTP Request nodes, or other nodes in their place | | What the caller gets back | \`Outcome\` and \`Respond 200 (invoice handled)\` | | Where failures go | \`Alert ops (Slack)\` | ### Example A supplier’s invoice arrives for 1,100 on a subtotal of 1,000. The supplier is in the master and its TRN matches. The total is not the subtotal plus 5%, so rule V-06 sends the invoice to review. The webhook answer lists the reason, and a ticket appears in your review queue. An invoice with a correct total and a matching purchase order posts a bill instead. ### For newcomers and experts **If you are new.** n8n draws a workflow as boxes joined by lines, and each box, a node, does one job. Here the boxes call your systems, and one Code box holds all the rules. Click Test workflow, send a sample invoice to the test URL and open each box’s output to see how the status was reached. **For experts.** The checks are plain JavaScript with no model in the loop, and the duplicate list lives in the workflow’s static data. Where to look closer | Node | What it does | What to know | | --- | --- | --- | | \`AI: extract fields from document\` | HTTP Request that posts the file name and a fixed \`application/pdf\` type | Your service must find the file by name, and every file is treated as a PDF | | \`Merge lookups\` | Joins the supplier list and the purchase orders | The Code node reads each list from its own node, not from the merged items | | \`Validate: TRN, duplicate, totals, PO match, limit\` | Runs the rules V-00 to V-09 and sets a status and reasons | A TRN of 15 digits, a VAT rate of 5% and AED limits are written into it | | \`Route by status\` | A Switch with the outputs \`AUTO\_APPROVE\`, \`REVIEW\` and \`REJECT\` | Each output goes to one HTTP Request, and all three meet again in \`Outcome\` | | \`Error trigger\` | Starts an alert when a run fails | Needs this workflow set as its own error workflow | ### Good to know The workflow posts bills on its own when every rule passes, and it extracts nothing by itself. - Not run: Mindket made no call to any API. It ran the validation code on sample invoices on its own machine and checked each rule - No extraction inside: the extraction route receives only a file name and a fixed \`application/pdf\` type, so your service must find the file by name - Built-in values: the TRN length, the VAT rate and the AED limits are in the code, so change them for your country - Duplicates: the list sits in the workflow’s static data. According to n8n’s documentation, static data is not saved when you run a workflow by hand, only for a published workflow that a trigger or webhook runs. The list never shrinks - Review: an invoice sent to review counts as seen, so sending it again after a fix is rejected as a duplicate - Webhook: it has no authentication, so anyone who learns the URL can send file names and cause bills to be posted - Automatic posting: a bill is posted as soon as every rule passes, so try it on a test system first - Error workflow: n8n’s documentation describes an error workflow as one that starts with the Error Trigger, and it does not say whether a workflow may name itself. Make one run fail to test it - Your data: the file name and the invoice fields go only to the API you put in \`base\` - Credentials: the JSON holds none ## README ```markdown # Supplier invoice checks and routing over your own REST APIs An n8n workflow that checks a supplier invoice and sends it where it belongs. A webhook receives the name of an invoice file. Your extraction service reads the document, and the workflow compares the result with your supplier list and open purchase orders. Next it posts the bill, opens a ticket for a person to check, or alerts accounts payable, and answers the webhook with the outcome. The workflow holds the rules and the routing, and nothing else. It has no AI model and no accounting system inside. Every outside system is a plain HTTP request to your own API, so you supply that API or swap each request for a node of your own system. ## What is inside - `workflow.json`: the workflow as n8n exports it, 18 nodes. 16 of them run and two are sticky notes. It holds no credential. - `README.md`: these notes. ## What we changed from the original copy - The address `https://api.your-company.example` in both `Config` nodes is now `https://`. - The two sticky notes no longer name the template's author or link to its site. They also no longer say the extraction step can call a model at `base`/llm/complete, because the step calls `base`/documents/extract. The notes now say what the nodes do, and ask you to save and press Publish instead of "Activate". - Nothing else. The rules, the thresholds and the routing are as they were. ## Before you start - An n8n instance, on n8n Cloud or your own server. The original's note asks for n8n 1.100 or later. - An API that answers the six routes below, or other n8n nodes that reach your systems. - A mailbox rule, a Drive watcher or an upload form that can send a POST to the webhook. - A few invoices to try. ## The routes the workflow calls Each route is called against the `base` address in `Config`. The nodes have no authentication, so add it to each one as your API needs. - `POST /documents/extract` with `{ "file_name": "...", "mime": "application/pdf" }`. It must answer `{ "fields": { supplier, invoice_no, date, trn, subtotal, vat, total, currency, confidence, line_items: [{ amount }] } }`. - `GET /accounting/suppliers`. It must answer `{ "rows": [{ supplier_name, trn, approved_limit_aed }] }`. - `GET /accounting/purchase_orders`. It must answer `{ "rows": [{ po_number, supplier, amount }] }`. - `POST /accounting/bills` with the checked invoice. It must answer `{ "bill_id": "..." }`. - `POST /review/queue` with the file, the status and the reasons. It must answer `{ "ticket": "..." }`. - `POST /alerts` with a channel and a text. Any answer will do. ## Set it up 1. In n8n, create a workflow, open its menu and choose Import from File. Pick `workflow.json`. 2. Open `Config` and replace `` in `base` with your API's host. Check `auto_approve_limit`, `ap_channel` and `total_tolerance`. Do the same for `base` in `Config (errors)`. 3. Add the authentication your API needs to each of the six HTTP Request nodes, or replace them with the nodes of your own systems. 4. Open the Code node `Validate: TRN, duplicate, totals, PO match, limit` and check the rules. The VAT rate is 5%, a TRN must have 15 digits, the confidence floor is 0.9, and the limits are in AED. 5. Save, press Publish at the top of the canvas (or Shift+P), and copy the Webhook URL. Point your mailbox or upload form at it. Anyone who has the URL can post to it, so keep it private. 6. In the workflow's settings, choose this workflow as the error workflow so that `Error trigger` sends an alert when a run fails. 7. Try a correct invoice first and then one whose total is off, and read the answer for each. ## How a run goes 1. `Webhook: invoice received (email, drive or upload)` takes a POST with a `file_name` in its body. 2. `Config` adds the `base` address, the limit for automatic approval, the alert channel and the tolerance for totals. 3. `AI: extract fields from document` posts the file name to your extraction route and gets the fields back. 4. `Accounting: supplier master` and `Accounting: open purchase orders` fetch the two lists, and `Merge lookups` joins them. 5. `Validate: TRN, duplicate, totals, PO match, limit` runs the rules, listed below, and sets a status and a list of reasons. 6. `Route by status` sends `AUTO_APPROVE` to `Accounting: post bill`, `REVIEW` to `Review queue: human check` and `REJECT` to `Slack: rejected, AP notified`. 7. `Outcome` builds a short answer with the status, the reasons and a bill id, a ticket or an alert flag. 8. `Respond 200 (invoice handled)` returns it to the caller. On any failure, `Error trigger` starts `Config (errors)` and `Alert ops (Slack)`, which posts a message to `/alerts`. The rules, each with its code: - V-00: the supplier or the invoice number is missing. Review. - V-01: the same supplier and invoice number were seen before. Reject. - V-02: the supplier is not in the master. Review. - V-03 and V-04: the TRN is not 15 digits, or differs from the master. Reject. - V-05: the lines do not add up to the subtotal, within the tolerance. Review. - V-06: the total is not the subtotal plus 5%, within the tolerance. Review. - V-07: the extraction confidence is below 0.9. Review. - V-08: the total is over the automatic approval limit and no purchase order matches. Review. - V-09: the total is over the supplier's own limit and no purchase order matches. Review. ## Change the look - The limits and the alert channel: `Config`. - Any rule, the VAT rate, the TRN length or the confidence floor: the Code node `Validate: TRN, duplicate, totals, PO match, limit`. - The routes and the systems behind them: the HTTP Request nodes, or your own nodes in their place. - What the caller gets back: `Outcome` and `Respond 200 (invoice handled)`. - Where failures go: `Alert ops (Slack)`. ## Good to know - Not run: Mindket made no call to any API. It ran the validation code on sample invoices on its own machine and checked each rule above. - Nothing extracts anything by itself. The extraction route receives only a file name and a fixed `application/pdf` type, so your service must be able to find the file by name, and every file is treated as a PDF. - The TRN length, the VAT rate and the AED limits are built into the code. Change them for your country before you rely on the checks. - The duplicate check keeps its list in the workflow's static data. According to n8n's documentation, static data is not saved when you run a workflow by hand, only for a published workflow that a trigger or webhook runs. The list also never shrinks. - An invoice sent to review counts as seen. Sending it again after a fix is rejected as a duplicate, so correct it in your review queue. - The webhook has no authentication. Anyone who learns the URL can send file names and cause bills to be posted, so protect it. - Posting a bill is automatic when every rule passes. Run it against a test system first. - The error workflow setting: n8n's documentation describes an error workflow as one that starts with the Error Trigger. It does not say whether a workflow may name itself, so make one run fail to test it. - Your data: the file name and the invoice fields go only to the API you put in `base`. - Credentials: the JSON holds none. ``` ## What is in it 3 files, 26 KB, downloaded as a zip. ```text NOTICE.md 724 B README.md 7 KB workflow.json 18 KB ``` ## Workflow check Checked by Mindket on 13 Nov 2026. Read from the workflow’s file, not from a run. - Steps: 16 steps, starting when its webhook is called or on its trigger node - AI: No step calls an AI model - Sign-ins: No sign-in - API keys: No API key is left in the file - Step types: Mindket’s checker reads all 8 of its step types ## Get it - [Get it on your Mindket account](https://account.mindket.com/account/?product=mindket#/market/2e5e5620-d005-44bd-986f-c3e5621abcd2) - [Its page on Mindket](https://mindket.com/p/2e5e5620-d005-44bd-986f-c3e5621abcd2)