Invoice & Accounts Payable Automation
End-to-end invoice processing automation — from email attachment ingestion to approval routing and ERP posting — eliminating 95% of manual data entry for a 150-person company.
The Problem
A 150-person manufacturing company's accounts team was processing 200–300 vendor invoices per month — all arriving as PDF email attachments. Each invoice required manual data extraction, matching against POs in Tally, getting department head approval over email, and manual posting. The process took 3–4 days per invoice cycle and had a 12% error rate.
Our Solution
An n8n workflow monitors a dedicated AP email inbox. When a PDF invoice arrives, it extracts the attachment, sends it to GPT-4o Vision for structured data extraction (vendor, invoice number, line items, amounts, tax), cross-references against open POs in Tally via API, routes to the relevant department head for WhatsApp approval (with extracted data + PO match shown), and on approval, posts directly to Tally with full audit trail.
Our Approach
Process Mapping
Documented the full AP workflow with the finance team: invoice arrival, data entry, PO matching, approval chain, and posting.
GPT-4o Vision Extraction
Tested GPT-4o Vision on 100 historical invoices to validate extraction accuracy. Achieved 96% accuracy on structured fields.
Tally API Integration
Built a custom Tally integration layer via the Tally ODBC connector and REST bridge to read POs and post invoices.
WhatsApp Approval Flow
Interactive WhatsApp messages showing invoice summary + PO match. Approve/reject/query via reply — with full conversation logged.
Exception Handling
Confidence scoring for each extracted field. Low-confidence invoices escalate to human review with the extracted data pre-filled.
The Results
| Metric | Before | After |
|---|---|---|
| Invoice Processing Time | 3–4 days | < 4 hours |
| Manual Data Entry | 200 hrs/month | 10 hrs/month |
| Error Rate | 12% | < 2.5% |
| AP Headcount | 3 FTEs | 1 FTE (redeployed) |
Tech Stack
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