Blog/Manufacturing

Automating the PO, GRN and Invoice Three-Way Match for Manufacturers

Match purchase orders, goods receipts and supplier invoices automatically, so AP pays the right amount on time and reviews only real mismatches.

By Sagar Makker · 5 min read · October 2026
In short
Manual three-way matching delays supplier payments and lets overbilling slip through
Read invoices automatically and match each line to PO and GRN within tolerances
Route only genuine price, quantity or tax mismatches to AP and purchase
The problem

Supplier invoices arrive by email, courier and the vendor portal. AP staff open the PO in the ERP, find the GRN from stores, and compare quantity, rate and tax line by line. Partial deliveries, rate revisions and missing GRNs turn each invoice into a chase across purchase, stores and the supplier.

The result is late payments, upset suppliers and missed early-payment discounts, alongside the opposite risk: invoices paid without a proper match because month-end is close. Duplicate invoices, rates above PO and GST details that do not match the purchase register slip through when everyone is rushing.

Why it happens
01Invoices arrive in many formats and are keyed into the ERP by hand
02GRNs are posted late by stores, so invoices wait with nothing to match
03No agreed tolerance rules, so every small difference becomes a query
04Rate changes and partial deliveries are not updated on the PO
How to fix it
1
Agree matching tolerances
Define acceptable variances for quantity, unit price and freight by category, such as a small rounding allowance. Anything inside tolerance is auto-approved; anything outside goes to review.
2
Capture invoices digitally
Read supplier name, GSTIN, invoice number, PO reference, line items, HSN codes, rates and taxes from each invoice, and check for duplicates by supplier and invoice number.
3
Match line by line
Compare each invoice line with the PO rate and the GRN quantity accepted by stores and quality. Handle partial deliveries by matching against cumulative received quantity.
4
Route exceptions to owners
Send price differences to purchase, quantity gaps to stores and tax mismatches to accounts, each with the three documents side by side and a clear question to answer.
Where an AI agent helps
Input
Supplier invoices, POs and GRNs from your ERP or Tally
Agent does
Extracts invoice data, checks duplicates and GST details, and matches each line to PO and GRN
Human gate
AP lead approves out-of-tolerance invoices and any change to payment amount
Outcome
Matched invoices ready for payment and a short exception queue
What to measure
Share of invoices matched without touchDays from invoice receipt to approvalDuplicate invoices caught before paymentInvoices waiting on a missing GRN
Questions
What is a three-way match?

It checks that the supplier invoice agrees with the purchase order, which fixes what you agreed to buy and at what rate, and the goods receipt note, which records what actually arrived and was accepted. Only then is the invoice approved.

What tolerance should we set?

There is no universal number. Set it per category based on rounding, freight variation and the value at risk. Many teams start strict, review which exceptions turned out harmless, and relax tolerances where the evidence supports it.

Does this replace our GST reconciliation?

No. It checks GST details on each invoice against the PO and supplier master. Reconciling input tax credit against GSTR-2B is a separate process, though matched invoice data makes it easier. Confirm the details with your tax advisor.

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