The outbound invoice checklist is behind you. This one is for the inbound side — specifically the failure modes that sit between a supplier's invoice, your shop floor's receipt, and the job cost report that your margin decisions depend on.
1. The GRN is where the match breaks — AP is just where you find out.
A blocked invoice in the AP queue usually traces back to a goods receipt note that was not posted, or was posted late. In a converting plant, a common scenario is a single supplier PO covering shipments to two plants: one plant posts its receipt immediately; the other holds because the substrate is under quality inspection. The consolidated invoice arrives, AP tries to match it, and one half cannot be reconciled. The exception belongs to the receiving dock, not to AP. If your process does not give AP visibility to GRN status before the invoice enters the queue, the exception will age there until someone tracks down its owner. Build the confirmation step upstream.
2. Know whether your substrate pricing is index-linked — and wire that into the match.
This is the most converting-specific failure mode in the brief. Packaging substrate contracts frequently set price via a formula referencing a published resin or containerboard index, often with a lag period and sometimes a cap or collar. The invoice states only a unit price. A standard three-way match compares that price to the PO and to the last invoice. It does not consult the index — it was never told to. An invoice can clear the match and still be wrong, with the variance between the contract formula and the billed amount invisible to any system not explicitly built to consume the index.
This matters most where the ERP manages substrate at moving-average price. When a supplier bills a surcharge the PO did not capture — an index adjustment that arrived after the PO was raised — the ERP may absorb the difference straight into the material master cost rather than surfacing it as a blocked invoice. The variance does not show up as a P&L item. It shows up as a gradually drifting material cost, found at physical inventory or margin review, by which point multiple jobs have been costed against an inflated MAP. Check your four converting-specific contract clauses before you go live with automated matching: index-linked pricing, tooling and die amortisation schedules, minimum order quantity penalties tied to SKU proliferation, and cube-based freight terms.
3. Freight does not belong to the three-way match — treat it separately.
A freight charge has no PO line and no corresponding goods receipt. It falls outside the match by design. For converters buying substrate by weight on a "freight included" price, variable freight adjustments may only surface at invoice time. What appeared to be the lowest-price supplier quote can cost more than alternatives once freight is separated and checked against the shipping contract or tariff schedule. At scale across a multi-facility freight programme, even a small reclassification rate becomes a recurring quarterly cost variance — and because it passes the match, nothing flags it automatically. Freight needs its own verification step, owned by someone with access to the shipping contracts.
4. Set your unit-of-measure translation in both systems, and treat it as maintained master data.
Substrate arrives by roll weight, is received in linear metres, consumed per job in square metres, and may be invoiced per thousand square inches. When the conversion logic between these levels is not centrally defined, discrepancies between the PO, the goods receipt, and the invoice are structurally inevitable — not exceptions, but guaranteed noise. In a MIS-to-ERP integration, the problem compounds: the MIS receipt is expressed in production units while the ERP AP module expects financial units matched to a PO line in its own item master. Without a live translation layer, every substrate receipt crossing from the MIS to the AP inbox carries a UOM ambiguity before it has even been touched. This is a master data maintenance obligation that grows with SKU count and supplier count. Assign an owner for the translation table in each system, and document what triggers a sync.
5. When a blanket PO release is revised after a partial receipt, verify that the already-matched lines are still correctly consumed.
If the ERP does not handle this cleanly, a revision can orphan an already-matched receipt or allow unused commitment to be reused. The resulting duplicate-payment risk looks, in the exception queue, like a routine partial-match exception. It is not. Flag any invoice arriving against a blanket PO where a release revision has occurred since the last goods receipt. The confirmation takes a minute. The duplicate-payment recovery does not.
6. When a supplier credit or return arrives, confirm the original receipt reversal and the job cost correction happen together.
A credit note that posts to AP without a corresponding reversal of the goods receipt leaves the job cost overstated. The AP balance corrects. The job does not. If the substrate return was quality-related — the inspection hold from tip one — the job that consumed the rejected material may be costing against substrate it was never actually charged for, or against substrate it was charged for and should not have been. The two corrections are logically one event. Build the process so they cannot be posted independently.
If any of these failure modes describe something already in your queue, we're glad to talk through how the integration between your MIS and your ERP can be built to handle them before they become a habit.