This Invoice Workflow Caught $47K In Overpayments Year One (12 Nodes) 🔥

Client processing 320 invoices monthly. Manual process. Someone opens email, downloads PDF, types into spreadsheet, checks PO, enters into accounting system.

One year running this workflow caught $47,000 in overpayments. Small discrepancies nobody noticed. $200 here. $500 there.

THE MANUAL DISASTER:

AP team rushing through 300+ invoices monthly. No time to verify every line item. Copy-paste errors. Decimal mistakes. PO mismatches missed.

When auditors found $47K in overpayments across the year, everyone blamed "human error." But humans can't verify 320 invoices perfectly every month.

THE DISCOVERY:

Built community template for invoice routing. Added document extraction at the front.

Now invoices get read automatically. Vendor, amounts, line items, PO references - all structured before any human touches it.

THE WORKFLOW:

Gmail trigger catches invoices → Get message downloads PDF attachment → Code renames binary for extraction → Document extraction pulls structured data → Code validates calculations and required fields → Sheets lookup matches PO number → Code checks 2% tolerance → IF routes approved or flagged → Sheets logs with status → Gmail confirms approved or alerts on flagged.

12 nodes. Runs automatically.

THE EXTRACTION + VALIDATION PATTERN:

Single extraction: Pulls everything. Invoice number, dates, vendor info, line items with quantities and prices, subtotal, tax, total, PO reference, payment terms, bank details.

Code validation: Checks calculations match. Line items total equals subtotal? Subtotal plus tax equals total? Required fields present? Flags discrepancies automatically.

One extraction. Code validates. Clean separation of concerns.

THE TRANSFORMATION:

Before: 2-3 hours daily processing invoices. Inconsistent validation. Errors discovered during audits weeks later.

After: 20 minutes daily reviewing flagged items only. Consistent validation every invoice. Anomalies caught immediately. Confirmations sent automatically.

THE NUMBERS:

320 invoices monthly processed

$47,000 overpayments identified year one

Mostly quantity mismatches and duplicate charges

One vendor billing for items never ordered

Human review: Exceptions only

UNEXPECTED BENEFIT:

Invoice with math that didn't add up got flagged instantly. Line items totaled $3,200 but invoice said $3,800. Previous process would have paid the wrong amount. Now validation catches calculation errors automatically.

Template in n8n and All workflows in Github

What validation rules would you add to catch overpayments?

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