What happens if a PO does not match an invoice?

When a PO doesn't match an invoice, payment stops until someone resolves the discrepancy — that's the whole point of matching. The standard check is the 'three-way match': PO (what you ordered) vs receiving record (what arrived) vs invoice (what you're billed). Common mismatches: price differences (supplier billed list price instead of agreed price), quantity differences (billed 100, received 90), substituted items, or freight charges that were never agreed.

Resolution is straightforward once visible: short delivery → supplier issues a credit note or adjusts the invoice; price discrepancy → point at the PO, which is why having one wins the argument; genuine change → document it and adjust the PO.

Without a PO, 'mismatch' isn't even detectable — you're just trusting the invoice. Most businesses that start matching find billing errors within the first month.