Why have our processing costs risen when volumes have not?
Processing costs usually rise with flat volumes for one of six reasons: the schemes changed their fees, a volume tier was not applied, a new behavioural fee such as Visa's VAMP started, a pass-through cost was marked up, FX was converted at a wider spread, or a charge was billed twice. Each leaves a different trace on the invoice.
Causes that start with the schemes
Visa and Mastercard change their fees several times a year, and they add fees that depend on how you process rather than how much. Both kinds of change raise cost per transaction without any change in volume. They arrive as scheme notices and new invoice lines, and they reach you directly or through your acquirer or sponsor.
Scheme fees changed
A scheme fee change raises the cost of every transaction it applies to, so a flat month can cost more with nothing else changed. Visa raised the base transmission fee paid by issuers and its misuse fee from January 2025 (Payments Dive). Mastercard is retiring its Acquirer Clearing Fee in favour of a new Network Access and Brand Usage fee (Moneris). Over a longer period, the UK Payment Systems Regulator found that core scheme and processing fees paid by acquirers rose by more than 25% in real terms between 2017 and 2023 (PSR final report, March 2025). A renamed fee line is often the first sign.
A new behavioural fee started
Behavioural fees are charged for how transactions behave, such as fraud and dispute rates, so they can grow while volume stands still. Visa's Acquirer Monitoring Program (VAMP) has charged acquirers $4 or $8 per fraudulent or disputed transaction above its thresholds since April 2025 (Visa VAMP fact sheet). The PSR reports acquirers saying that behavioural fees they cannot understand cost them "hundreds of thousands of pounds" (PSR PS26/1, July 2026).
Causes in your contracts and invoices
The other four causes sit between your processing agreements and the invoices billed under them. The contract says one thing and the billing system does another, usually because a rate, a tier or a conversion was set up once and never revisited. These are the discrepancies a recalculation from the contract finds and a glance at the invoice does not.
A volume tier was not applied
Tiered pricing steps the rate down once volume passes a breakpoint. If the processor's billing keeps the old band, cost per transaction stays high even as the contract says it should fall. A tier can also be lost when volume is split across merchant IDs or legal entities that the contract counts together, or when the band resets at a contract anniversary that the billing system dates differently.
Pass-through costs were marked up
Where an acquirer, processor or BIN sponsor passes scheme fees on to you, a mark-up can hide inside a line labelled "scheme fees". A large merchant told the Reserve Bank of Australia that different acquirers charged it different scheme fees "for like-for-like transactions despite having an interchange++ plan" (RBA summary of submissions, 2025). Sponsored card programmes often pay one per-transaction price that bundles scheme assessments, processor fees and the sponsor's margin (Marqeta UK guide).
FX was converted at a wider spread
An FX mark-up above the contracted spread, or a second mark-up on top of scheme conversion, raises cost on cross-border volume without any change in count. Spreads are hard to see from the outside: the Financial Stability Board's 2025 progress report notes only "partial transparency on fees, FX spreads" in cross-border payments (FSB, October 2025). A shift in your mix towards cross-border cards has the same effect, so separate the two.
A charge was billed twice
Duplicate charges appear when a refunded or re-presented transaction is charged a second processing fee, when a payout retry is billed as a new payout, or when a fixed monthly fee lands on two invoices. Each one is small against the whole bill, which is why duplicates survive a review of totals. They show up when invoice line counts are compared with transaction counts.
How to check it yourself
You can find where a rise came from with two months of invoices, the matching transaction files and your processing agreements. Split the cost into its layers, find the layer that moved, then recalculate a sample of transactions from the contract clause. The method takes a few days in a spreadsheet for one processor.
Scheme invoices need care: non-transactional scheme fees arrive one to two months in arrears and are calculated on aggregates (Adyen help), so match each invoice to the activity month it charges for.
Pick two comparable months
Choose two months with similar transaction counts and value. Collect every invoice from each processor, acquirer, sponsor and scheme for both, plus the transaction files.
Split cost into layers
For each month, work out cost per transaction and cost as a share of value for interchange, scheme fees, acquirer or processor fees and FX. The layer that moved tells you where to look.
Compare the invoices line by line
Within that layer, look for new line names, changed unit rates, lines that appear twice, and lines whose count is higher than the number of transactions they should apply to.
Recalculate a sample from the contract
Take 20 to 50 transactions of the type that moved. Find the clause that sets each fee, calculate what it should have been, and compare it with what was billed.
Check tiers and minimums
Calculate the month's qualifying volume the way the contract defines it, including which entities and merchant IDs count, and confirm the band and any minimum that was applied.
Write each finding down with its evidence
Record the clause, the transaction rows and the amount for every difference. That is what a processor will ask for when you raise it.
Why a one-off check misses it
A one-off check tells you whether one month was right. Fee schedules keep changing, so an error introduced the month after the check runs unseen until someone checks again. A sample also misses small per-transaction overcharges that only become material once they are added up across every transaction.
The Reserve Bank of Australia recorded that some PSPs "absorb" fee inaccuracies rather than investigate them, because of the complexity and the frequency of revisions (RBA conclusions, March 2026). Submissions to the same review describe fee schedules "often 400 pages long" with "up to 800 categories of fees" (RBA summary of submissions, 2025). A manual check of that material is expensive to repeat, so it tends to happen once, at a renewal or after a surprise.
How FeeVerify catches it as it lands
FeeVerify recalculates every transaction against a rulebook built from your own contracts and splits any change in cost by layer, counterparty and cause. With optional continuous assurance it runs on each new month of data, so a scheme notice, a downgrade, a lost tier or a duplicate fee shows up in the month it starts, with the clause and the rows behind it.
AI reads the contracts and does the recalculation, so you need no new headcount. Each rule carries a confidence grade, and experienced payments specialists sign off every material finding before anyone acts on it. In an anonymised engagement for a tier-one cross-border payments business operating across multiple markets (blended and IC++ acquiring), this method traced a six-figure recurring variance to a single contract clause (see the proof).
Sources: PSR final report, March 2025; PSR PS26/1, July 2026; Payments Dive on Visa fees from January 2025; Moneris network fee updates; Visa VAMP fact sheet, 2025; RBA summary of submissions, 2025; RBA conclusions on scheme fees, March 2026; Marqeta UK guide to card programme costs; FSB progress report, October 2025; Adyen help on non-transactional scheme fees.
Start with one month of your own data.
A pilot begins with the agreements that protect both sides, then your contracts and one month of settlement data, scoped with a payments specialist on the first call. The 30-day diagnostic re-costs every transaction against them and shows each variance with its clause, before any recurring fee.