Insights · Payment cost · November 2026

Interchange++ invoice check: how to find the fees you are paying but should not be.

Interchange++ is sold as transparency. It is only transparent if someone reconciles the invoice. In my experience almost nobody does, which is why a line-level check pays for itself in the first month.

What Interchange++ promises

Under Interchange++ you pay three components per transaction: the interchange fee set by the scheme and paid to the issuer, the scheme fees paid to Visa or Mastercard, and the acquirer's margin. The first two are published, or at least determinable, and the third is in your contract. The promise is that every line can be checked. The reality is that the invoice arrives as a PDF with aggregated lines, the interchange tables run to hundreds of rows per scheme and region, and the person who negotiated the contract has usually moved on.

Where the overcharges hide

  • Interchange qualification. Transactions downgraded to a higher interchange category because of missing data, late settlement, wrong MCC, or a token or 3DS flag that did not carry through. The difference between a qualified and a downgraded rate on a consumer card in Europe is small per transaction and large per year.
  • Scheme fees nobody itemised. Cross-border assessments, authorisation fees, acquirer licence fees, integrity and misuse fees, and the long tail of per-transaction and per-decline charges. Some are legitimately passed through; some are passed through at a mark-up that the contract does not allow.
  • Margin applied to the wrong base. Acquirer margin agreed in basis points on net volume, invoiced on gross volume including refunds and declined attempts.
  • Currency conversion. Settlement in a currency other than the transaction currency, with the conversion spread buried in the exchange rate rather than shown as a fee.
  • Fees that survived renegotiation. A rate was reduced in the latest contract and the billing system was never updated. This is the most common finding and the easiest to recover.
  • Minimums, reserves and the interest on them. Monthly minimum charges applied after volume passed the threshold, rolling reserves held beyond the agreed period, and no interest where the contract provides for it.

The method

  1. Get the data at transaction level. Not the PDF. The settlement or fee file from each acquirer, one row per transaction and fee, with interchange category, scheme fee codes and FX rate where applicable. If the acquirer cannot provide it, that is a finding in itself.
  2. Rebuild the expected cost. For each transaction, look up the interchange category the transaction should have qualified for, apply the published rate, add the scheme fees that legitimately apply, and add the contracted margin on the contracted base.
  3. Compare, line by line. The differences fall into a short list of patterns: downgrades, mark-ups, wrong base, FX spread, stale rates. Group by pattern and quantify each.
  4. Separate recoverable from fixable. Stale rates and wrong bases are usually recoverable retrospectively. Downgrades are fixable going forward by correcting the data you send. FX spread is a negotiation.
  5. Automate the check. Once the rebuild logic exists, run it on every invoice. This is where AI-assisted tooling earns its place: classifying fee lines, matching interchange categories and flagging anomalies against the previous month is exactly the kind of repetitive, rule-heavy work it does well, with a person reviewing the exceptions.

What a check typically finds

Across advisory engagements since 2019 the usual pattern is 10 to 15% lower processing cost within the first month, part from recovered overcharges and part from corrected qualification. For one listed group, moving every acquirer and PSP onto Interchange++ and reconciling the result removed more than €4m a year. The size of the finding scales with volume and with the number of years since anyone last looked.

Doing it without upsetting the acquirer

A good acquirer expects to be checked and corrects errors without argument. Present findings as a reconciliation, not an accusation. Agree the method before the number. Ask for the fee file as a standing monthly deliverable. The relationship usually improves, because the conversation shifts from "your fees are high" to "line 412 does not match clause 7.3".

I run this check as part of a fractional Head of Payments engagement or as a stand-alone review. Bring one month of fee files to a call and I will tell you what it would find.