Automate timesheet to invoice conversion with OpenAI, Gmail & Google Workspace

This workflow converts emailed timesheets into structured invoice rows in Google Sheets and stores them in the correct Google Drive folder structure.

It:

• Listens to Gmail for timesheet attachments
• Runs OCR and AI parsing
• Looks up Customer and PO data from a Google Sheet
• Organizes files in Client → Employee → Year folders
• Reuses an existing invoice sheet or creates a new one and writes the invoice row

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Quick Implementation Steps

1. Import the workflow JSON into your n8n instance.
2. Set up credentials for:
   • Gmail
   • Google Drive
   • Google Sheets
   • OpenAI
3. Check the OCR HTTP node:
   • Default URL: https://universal-file-to-text-extractor.vercel.app/extract
4. Configure "Get Customer Info From PO Sheet" with:
   • Spreadsheet ID
   • Correct sheet and column names
5. Confirm Gmail Trigger filter:
   • has:attachment (filename:timesheet OR subject:timesheet) and unread only
6. Ensure your Client Invoices root folder exists in Google Drive.
7. Test once with a sample timesheet email.
8. Activate the workflow.

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What It Does

• Reads unread Gmail messages with timesheet attachments.
• Splits and processes each attachment separately.
• Sends files to OCR and converts them to text.
• Uses OpenAI to extract:
  • Employee Name
  • Client Name
  • Week Start and End Dates
  • Total Billable Hours
  • Current Year
• Looks up Customer and PO data from a Google Sheet:
  • Account Number
  • PO Number
  • Item Name
  • Folder Name
  • Invoice range
  • Due Date offset
• Builds or finds:
  • Client folder
  • Employee folder
  • Year folder
• Either:
  • Appends to an existing sheet for that employee and period, or
  • Creates a new sheet, sets timezone, moves it into the right folder, and adds the invoice row

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Who Is It For

• Agencies and consultancies billing from emailed timesheets
• Finance or ops teams managing many clients and employees in Google Workspace
• Service providers that keep one sheet per employee per period
• Anyone who wants to stop manually reading timesheets and filling invoice sheets

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Requirements

• n8n instance
• Gmail account with timesheet emails
• Google Drive and Google Sheets
• OpenAI API key
• OCR API endpoint (or the default one)
• Customer POs Google Sheet with:
  • Email
  • Customer Account Number
  • PO Number
  • Item
  • Folder Name
  • Invoice range
  • Due Date Calculation

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How It Works

1. Email Intake and Loop

• Gmail Trigger
  • Polls every minute
  • Filter: unread + has attachment + timesheet in file name or subject
• Split Binary Attachments
  • Creates one item per attachment
• Loop: Process Each Attachment
  • Handles each timesheet file in sequence

2. OCR and AI Parsing

• Extract Text from Attachment
  • Sends binary file to OCR endpoint
  • Returns plain text
• Extract Timesheet Data (OpenAI)
  • Reads the text and outputs strict JSON with:
    • Employee Name
    • Client Name
    • Week Starting Date
    • Week Ending Date
    • Total Working Hours
• Set Timesheet JSON Fields
  • Normalizes and stores:
    • Employee Name
    • Total Billable hours
    • Week Start Date and Week End Date
    • Client Name
    • Current Year

3. Customer and PO Lookup

• Get Customer Info From PO Sheet
  • Looks up sender email
  • Pulls:
    • Customer Account Number
    • PO Number
    • Item
    • Folder Name
    • Invoice range
    • Due Date Calculation

4. Drive Folder Discovery

• Search: Client Invoices Folder
  • Finds the main invoices root folder
• Search or create:
  • Client folder using Client Name
  • Employee folder using Folder Name from PO sheet
• Search: Year Folder
  • Looks for folder matching Current Year
• If Year Folder does not exist:
  • Create Year Folder or Create Current Year Folder
• Set: Invoice Range
  • Stores invoice range and Year Folder id

5. File Naming and Sheet Search

• Set: File Name from Start and End Based Date Range
  • Builds:
    • File Name (Start Date Based)
    • File Name (End Date Based)
  • Handles weekly and 15 days invoice logic
• Search: File By Start Date Name
• Search: File By End Date Name
• Merge: Combine Folder Search Results
  • Merges both search results
• If: Invoice Range is 15 Days
  • Uses custom 2 week window for file naming
• Set Invoice Date and Due Date Days
  • Invoice Date from week end
  • Due Date from week end plus offset

6. Reuse vs Create Sheet

• If: File Already Exists
  • If found
    • Go to Append: Final Row to Existing Sheet
  • If not found
    • Go to Sheets: Create Sheet

New Sheet Path

• Sheets: Create Sheet
  • Creates new spreadsheet with generated name
• HTTP Request (create sheet)
  • Sets spreadsheet timezone to America/New_York
• Drive: Move Sheet To Final Folder
  • Moves spreadsheet into the Year Folder
• Set: Empty Row Structure
  • Prepares JSON structure for invoice row
• Sheets: Append Row1
  • Writes the first invoice row
• Set: Spreadsheet (ID and Name)
  • Stores id and name
• Append: Final Row to Existing Sheet
  • Ensures row is appended with full mapping

Existing Sheet Path

• Set: Spreadsheet (ID and Name)
  • Uses found spreadsheet
• Append: Final Row to Existing Sheet
  • Appends new row with:
    • Customer Account Number
    • Invoice Date
    • Due Date
    • PO Number
    • Item and columns
    • Total billable hours as Quantity
    • Description with week period

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How To Set Up

1. Import and Credentials

• Import JSON in n8n
• Set credentials for:
  • Gmail Trigger
  • Google Drive nodes
  • Google Sheets nodes
  • OpenAI node
  • OCR HTTP node if needed

2. Customer POs Sheet

• In Get Customer Info From PO Sheet:
  • Set Spreadsheet ID
  • Confirm column names
• Make sure each employee email row has:
  • Customer Account Number
  • PO Number
  • Item
  • Folder Name
  • Invoice range
  • Due Date Calculation

3. Drive and Gmail

• Confirm Client Invoices root folder exists
• Confirm Gmail Trigger:
  • Query string
  • Poll schedule

4. Test

• Send a sample timesheet email
• Run the workflow once manually
• Check:
  • Folder structure
  • Created or reused sheet
  • Invoice row content

5. Activate

• Turn workflow ON once tests are successful.

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How To Customize

• Swap the OpenAI model in Extract Timesheet Data.
• Change prompt to extract extra fields such as project, cost center, or approval status.
• Replace OCR endpoint with another service if needed.
• Change folder naming rules in Set and Create folder nodes.
• Adjust file naming rules for different billing periods.
• Add validation steps to handle:
  • Missing name
  • Zero hours
  • Invalid dates
• Extend the PO sheet and invoice sheet with:
  • Hourly rate
  • Currency
  • Tax codes

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Use Case Examples

• Weekly consulting invoices from signed timesheets.
• Contractor billing for staffing agencies.
• Internal cross charging between departments using timesheet reports.
• Creating a clean, auditable history of timesheets and related invoice lines.

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Troubleshooting Guide

Issue	Possible Solution
No rows are created	Check Gmail Trigger is active and the filter matches the email. Confirm email is unread and has attachments.
OCR returns empty or error	Check OCR URL, status code, and supported file types. Log the response body.
Wrong or missing dates or hours	Review OpenAI prompt and a sample output. Ensure JSON keys in Set Timesheet JSON Fields match the AI output.
Folders not found or created	Confirm the Client Invoices root exists and that Client Name and Folder Name text matches what the workflow expects.
Files in wrong year folder	Check Current Year extraction and Year Folder search logic.
Duplicate sheets for same period	Check file naming code and Drive search nodes for exact match on names.
Due Date incorrect	Confirm Due Date Calculation in PO sheet and date math formats in Set and append nodes.

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Need Help or More Workflows?

Want to customize this workflow for your business or integrate it with your existing tools?
Our team at Digital Biz Tech can tailor it precisely to your use case from automation logic to AI-powered enhancements.

We can help you set it up for free — from connecting credentials to deploying it live.

Contact: [email protected]
Website: https://www.digitalbiz.tech
LinkedIn: https://www.linkedin.com/company/digital-biz-tech/
You can also DM us on LinkedIn for any help.

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