# Block duplicate vendor invoice payments with Google Sheets: n8n workflow

> Started by another system calling it, and works across Gmail, Google Sheets and Slack. 20 steps, 3 branches: a working afternoon to understand properly.

Source: https://millionrounds.com/workflow/block-duplicate-vendor-invoice-payments-with-google-sheets-2 (Millionrounds; every figure on the page links to its filing or article)

[Automation library](https://millionrounds.com/workflows) · [Money admin](https://millionrounds.com/workflows?category=Money+admin#library)

# Block duplicate vendor invoice payments with Google Sheets

Started by another system calling it, and works across Gmail, Google Sheets and Slack. 20 steps, 3 branches: a working afternoon to understand properly.

Medium

[Download free](https://millionrounds.com/login?next=%2Fapp%2Fworkflow%2Fblock-duplicate-vendor-invoice-payments-with-google-sheets-2)

**20 steps** Medium: a working afternoon

**3** Branches: places the flow splits

**0** Loops or waits

**3** Services it connects to

## The flow

Starts it 4 Logic 7 Service 9

The steps in the order they run, from what starts it.

- 1 **Webhook, JSON Invoice** Webhook *Starts it*
- 2 **Webhook, PDF Invoice** Webhook *Starts it*
- 3 **Merge Intake Paths** Merge *Logic*
- 4 **OCR, Extract Invoice Fields** Http Request *Service*
- 5 **Parse Invoice Payload** Code *Logic*
- 6 **Is Valid Invoice** If *Logic*
- 7 **Lookup Existing Invoice** Google Sheets *Service*
- 8 **Flag Duplicate Status** Set *Logic*
- 9 **Duplicate Found** If *Logic*
- 10 **Slack, Duplicate Alert** Slack *Service*
- 11 **Teams, Duplicate Alert** Http Request *Service*
- 12 **Prepare Approval** Set *Logic*
- 13 **Log Duplicate to Sheet** Google Sheets *Service*
- 14 **Register Unique Invoice** Google Sheets *Service*
- 15 **Respond, Duplicate Blocked** Respond To Webhook *Starts it*
- 16 **Push to ERP System** Http Request *Service*
- 17 **Needs Approval** If *Logic*
- 18 **Respond, Invoice Accepted** Respond To Webhook *Starts it*
- 19 **Email, Manager Approval** Gmail *Service*
- 20 **Slack, Cleared Notice** Slack *Service*

## How it's built

- **Starts on:** Another system calling it
- **Steps:** 20, with 3 branches
- **Size:** Medium: a working afternoon
- **Connects to:** Gmail, Google Sheets, Slack
- **Model:** None. This is plumbing, not judgement

## Questions

What does it need to run?

An n8n account, plus your own Gmail, Google Sheets and Slack accounts. You connect your own accounts after importing it; none are included.

What starts it?

It starts on another system calling it.

Does it use AI?

No. Every step is fixed logic or a call to a service, so it does the same thing every time.

How long does it take to set up?

Plan an afternoon. 20 steps is enough that you should read each one before running it.

How do I import it?

Copy the workflow, open a new workflow in n8n and paste. The steps appear on the canvas, ready for your own accounts.

**Before you run it**

Nothing here has been tested by us. It is somebody's working automation, read and described from its own steps. Treat the connections it wants as a list of accounts it will touch, and read the 20 steps before you point it at anything that matters.

## Run it in n8n

- **Create your n8n account** Free to start. n8n is where the workflow runs. [Create an n8n account ↗](https://millionrounds.com/n8n)
- **Download the workflow** Free with a Millionrounds account. [Download free](https://millionrounds.com/login?next=%2Fapp%2Fworkflow%2Fblock-duplicate-vendor-invoice-payments-with-google-sheets-2)
- **Paste it into n8n** Open a new workflow in n8n and paste. Then connect your own accounts.

Stored with the author's traces removed: canvas notes, instance identifiers, saved credential names and any live document they had left behind.

## Connects to

Each opens the other workflows that use it.

[Gmail](https://millionrounds.com/workflows?service=Gmail#library)[Google Sheets](https://millionrounds.com/workflows?service=Google+Sheets#library)[Slack](https://millionrounds.com/workflows?service=Slack#library)

## Workflows like it

Also money admin, with the same services where possible, closest in size first.

- [**Automate invoice processing with Gmail and OCR.space** 20 steps · Gmail, Google Sheets](https://millionrounds.com/workflow/automate-invoice-processing-with-gmail-and-ocr-space)
- [**Create and upload YouTube videos with FFmpeg** 20 steps · Google Drive, Google Sheets](https://millionrounds.com/workflow/create-and-upload-youtube-videos-with-ffmpeg)
- [**Deliver photography galleries after payment with Razorpay** 20 steps · Airtable, Gmail](https://millionrounds.com/workflow/deliver-photography-galleries-after-payment-with-razorpay)
- [**Reconcile bank payments with ERP and Google Sheets** 20 steps · Google Sheets, Slack](https://millionrounds.com/workflow/reconcile-bank-payments-with-erp-and-google-sheets)
- [**Collect invoices from Gmail and save them** 20 steps · calls a model · Gmail, Google Drive](https://millionrounds.com/workflow/collect-invoices-from-gmail-and-save-them)
- [**Extract and log invoice data to Google Sheets with Ainoflow** 20 steps · calls a model · Gmail, Google Sheets](https://millionrounds.com/workflow/extract-and-log-invoice-data-to-google-sheets-with-ainoflow)