# Send milestone billing invoices with Google Sheets and OpenAI: n8n workflow

> Started by a clock, and works across Gmail, Google Sheets and Slack. It hands the judgement calls to OpenAI.

Source: https://millionrounds.com/workflow/send-milestone-billing-invoices-with-google-sheets-and-opena (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)

# Send milestone billing invoices with Google Sheets and OpenAI

Started by a clock, and works across Gmail, Google Sheets and Slack. It hands the judgement calls to OpenAI. 16 steps, 2 branches: a working afternoon to understand properly.

Medium Calls a model: OpenAI

[Download free](https://millionrounds.com/login?next=%2Fapp%2Fworkflow%2Fsend-milestone-billing-invoices-with-google-sheets-and-opena)

**16 steps** Medium: a working afternoon

**2** Branches: places the flow splits

**0** Loops or waits

**3** Services it connects to

## The flow

Starts it 2 Model 1 Logic 6 Service 7

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

- 1 **On Workflow Error** Error trigger *Starts it*
- 2 **Schedule – Poll Milestones1** Schedule trigger *Starts it*
- 3 **Slack – Send Error Alert** Slack *Service*
- 4 **Sheets – Read Milestones1** Google Sheets *Service*
- 5 **Filter – Ready to Invoice1** Code *Logic*
- 6 **IF – Skip if None Ready1** If *Logic*
- 7 **Code – Calculate Billable Amount1** Code *Logic*
- 8 **GPT-4o – Write Invoice Narrative1** Open Ai *Model*
- 9 **Code – Merge GPT + Build Approval URL1** Code *Logic*
- 10 **Code – Generate HTML Invoice1** Code *Logic*
- 11 **Gmail – Send Invoice to Client1** Gmail *Service*
- 12 **If1** If *Logic*
- 13 **Sheets – Mark Invoice as Sent1** Google Sheets *Service*
- 14 **Sheets – Log Invoice1** Google Sheets *Service*
- 15 **Sheets – Update Approval Status1** Google Sheets *Service*
- 16 **Slack – Notify Accounts Team1** Slack *Service*

## How it's built

- **Starts on:** A clock
- **Steps:** 16, with 2 branches
- **Size:** Medium: a working afternoon
- **Connects to:** Gmail, Google Sheets, Slack
- **Model:** OpenAI

## Questions

What does it need to run?

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

What starts it?

It starts on a clock.

Does it use AI?

Yes. It calls OpenAI. Model calls are billed by the provider, not by n8n.

How long does it take to set up?

Plan an afternoon. 16 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 16 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%2Fsend-milestone-billing-invoices-with-google-sheets-and-opena)
- **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 bank statement and invoice reconciliation** 16 steps · calls a model · Google Sheets](https://millionrounds.com/workflow/automate-bank-statement-and-invoice-reconciliation)
- [**Automate job discovery & AI proposals across Upwork, Freelancer** 16 steps · calls a model · Gmail, Google Sheets](https://millionrounds.com/workflow/automate-job-discovery-and-ai-proposals-across-upwork-freela)
- [**Automated invoice processing & filing with IMAP** 16 steps · calls a model · Email, Google Drive](https://millionrounds.com/workflow/automated-invoice-processing-and-filing-with-imap)
- [**Automated sales proposal & summary generator with OpenAI** 16 steps · calls a model · Gmail, Google Drive](https://millionrounds.com/workflow/automated-sales-proposal-and-summary-generator-with-openai)
- [**Expense Logging with Telegram and Text Parsing** 16 steps · calls a model · Google Sheets, Telegram](https://millionrounds.com/workflow/expense-logging-with-telegram-and-text-parsing)
- [**Extract invoice data from Gmail to Airtable with Mistral** 16 steps · calls a model · Airtable, Gmail](https://millionrounds.com/workflow/extract-invoice-data-from-gmail-to-airtable-with-mistral)