Fee leakage is not one problem. It is six recurring patterns, and almost every overcharge a fintech finance team will ever find is one of them. Naming the pattern is the first step to catching it, because a discrepancy you can categorize is one you can track, prove, and dispute. This is the taxonomy: the six categories of PSP discrepancy, what each one is, how it happens, and what it takes to prove it.
TL;DR
- Nearly every PSP fee discrepancy falls into one of six categories: rate deviation, fee overcharge, FX markup, missing fee, duplicate fee, and timing violation.
- Rate deviation, the wrong rate applied, is the single most common. FX markup, hidden inside the exchange rate, is usually the most expensive.
- A "missing fee" in a leakage context usually means a credit or rebate you are owed that the provider left off, the only category where the error is an omission.
- Each category has a typical cause and a specific kind of evidence that proves it. Recovery depends on the evidence, not the suspicion.
- Operator terms like tier misapplication and settlement deduction error are not separate categories; they are common causes that show up as rate deviations, overcharges, or duplicates.
- Classifying discrepancies by category is what lets a team measure where leakage concentrates and which disputes are worth pursuing.
Short answer
PSP fee discrepancies fall into six categories. A rate deviation is when the provider applies a different rate than the contract specifies. A fee overcharge is when a specific fee is billed at a higher amount than agreed. An FX markup is when the margin on a currency conversion exceeds the contracted spread. A missing fee is a charge or, more often, a credit the contract specifies that does not appear, typically an omitted rebate owed to you. A duplicate fee is the same charge billed more than once. A timing violation is a charge raised outside the window the contract allows. Together these account for almost every discrepancy a fintech finance team encounters, and each has a distinct cause and a distinct form of evidence required to dispute it.
The six categories at a glance
| Category | What it is | Common cause | Example | Evidence that proves it |
|---|---|---|---|---|
| Rate deviation | Wrong rate applied to a transaction | Tier misapplication, wrong corridor, stale contract version | Contract sets 35 bps on a band; the provider charges 42 | The transaction, the contracted rate, and the charged rate |
| Fee overcharge | A discrete fee billed too high | Inflated fixed fee, missed discount, settlement deduction | A contracted $0.35 payout fee billed at $0.42 | The contracted amount, the billed amount, and the line item |
| FX markup | Conversion margin above the contracted spread | Excess margin, bad reference timestamp, layered markup | A 25 bps contracted spread received as 54 bps | The mid-market rate, the received rate, and the contracted spread |
| Missing fee | A specified charge or credit absent | Omitted rebate, discount, or corridor reduction owed to you | A volume rebate owed after a threshold, never applied | The entitlement clause, the trigger conditions, and its absence on the invoice |
| Duplicate fee | The same charge billed twice | Double-billing, invoice-plus-settlement, repeated line | One payout's processing fee charged twice | The two charges, one underlying event, and a single-charge clause |
| Timing violation | A charge outside its contractual window | Pre-ramp minimum, excluded period, wrong date | A monthly minimum charged during a fee-free ramp | The charge, its date, and the window or condition clause |
Why a taxonomy matters
A finance team that describes its provider charges as "probably a bit high" cannot do anything with that. A team that can say "this is a rate deviation of seven basis points on the euro corridor, here is the contract clause and here is the transaction" can recover money. The difference is categorization.
Naming the six patterns does three things. It makes leakage measurable, because you can see how much sits in each category and where to focus. It makes disputes winnable, because each category implies the specific evidence a provider will require. And it makes the work trackable, because resolution rates and recovery can be reported by type. The categories below are the ones a verification system uses to classify every discrepancy it finds.
1. Rate deviation
What it is: the provider applied a different rate than your contract specifies for that transaction. This is the percentage or basis-point rate on a variable fee, such as a processing fee or a per-transaction charge.
How it happens: the most common cause is tier misapplication, where the provider's billing system applies the wrong volume band, often defaulting to a more expensive tier when contract metadata is missing on their side. Other causes include the wrong corridor rate, or a rate from a superseded contract version applied after an amendment.
Example: your contract specifies 35 basis points on a transaction band and the provider charges 42. Small per transaction, six figures across a quarter of volume.
How to prove it: the transaction, the contracted rate for its specific properties, and the rate actually charged, side by side. Rate deviation is the single most common discrepancy category, precisely because the error is invisible at the level of any one transaction.
2. Fee overcharge
What it is: a specific fee billed at a higher amount than the contract allows. Where a rate deviation is about the rate applied to a value, an overcharge is about the amount of a discrete fee, often a fixed or flat charge.
How it happens: a fixed per-transaction fee billed above its contracted amount, a flat monthly fee inflated, a charge applied where a contracted discount should have reduced it, or a settlement deduction taken at a higher amount than agreed.
Example: the contract sets a fixed payout fee of $0.35 and the invoice bills $0.42, or a flat platform fee comes through above its agreed figure.
How to prove it: the contracted amount for the fee, the amount billed, and the line item connecting them. The distinction from rate deviation matters for disputes because the provider will resolve a wrong rate and a wrong fixed amount through different parts of their billing logic.
3. FX markup
What it is: the margin on a currency conversion exceeds the spread your contract allows. It is usually the most expensive category and the hardest to see, because the margin is built into the exchange rate rather than shown as a fee.
How it happens: the realized spread between the mid-market reference rate and the rate you received is wider than your contracted basis points, whether through excess margin, an unfavorable reference timestamp, or markup layered on an already-marked rate.
Example: your contract allows 25 basis points over mid-market and the conversion you received works out to 54, with the difference hidden inside a single blended rate.
How to prove it: the mid-market reference rate at the moment of conversion, the rate you received, the implied spread, and your contracted spread. This requires reconstructing the reference rate, which is why FX markup is the discrepancy almost no one checks. It is covered in depth in the comparison of FX spread versus FX markup.
4. Missing fee
What it is: a charge or credit the contract specifies that does not appear on the invoice. In a leakage context this almost always means a credit owed to you, such as a volume rebate, a performance discount, or a corridor-specific reduction, that the provider has quietly omitted.
How it happens: the rebate or discount your contract entitles you to is simply left off. Because nothing is shown, nothing prompts you to question it. This is the only category where the error is an absence rather than a wrong number.
Example: your contract grants a volume rebate once you cross a threshold, you cross it, and no rebate line appears.
How to prove it: the contract clause establishing the entitlement, the conditions that triggered it, and its absence from the invoice. Catching it requires knowing your own entitlements well enough to notice when they are missing, which is exactly why omitted credits are among the most reliably missed items on any invoice.
5. Duplicate fee
What it is: the same charge billed more than once.
How it happens: a transaction charged twice in the same period, a fee that appears on both an invoice and a settlement deduction, or the same charge carried across two consecutive invoices through a billing-system error.
Example: a single payout incurs its processing fee twice, or a fee netted from settlement also appears as an invoice line.
How to prove it: the two charges, the single underlying transaction or event they both reference, and confirmation that the contract provides for the fee only once. Duplicates are among the most straightforward discrepancies to win once surfaced, because the evidence is unambiguous.
6. Timing violation
What it is: a charge raised outside the window the contract permits. These are clause violations rather than arithmetic errors.
How it happens: a fee billed in a period the contract excludes, a monthly minimum applied before a contractual ramp period ends, or a charge dated outside its valid window. The amount may be correct in isolation; the timing is not.
Example: a minimum monthly fee charged during a three-month ramp the contract says should be fee-free.
How to prove it: the charge, its date, and the contract clause defining the window or condition it breached. Timing violations only surface if you check the date and the period against the contract, which manual review rarely does consistently.
A note on operator terms
Several terms finance teams use day to day are not separate categories but causes that surface as one of the six. Tier misapplication is a common cause of a rate deviation or a fee overcharge. A settlement deduction error usually presents as a fee overcharge or a duplicate fee, distinguished mainly by the fact that the money was taken at settlement rather than billed. Rebate omission is a missing fee. Mapping the language you use onto the six categories is part of what makes leakage trackable, because a provider will not accept "this feels wrong," only "this is a duplicate, here is the evidence."
Why classification drives recovery
The reason to insist on these categories is not tidiness. It is that recovery is an evidence game, and each category names the evidence the provider will demand. A discrepancy you can classify is a discrepancy you can attach the transaction, the clause, and the variance to, which turns a suspicion into a claim. It also lets a team see where its leakage actually lives, whether the money is mostly in FX markup or mostly in rate deviations, and aim its effort accordingly. A verification system earns its place here by classifying every discrepancy into one of these categories automatically and attaching the evidence each one requires, which is what platforms such as Bluefyn are built to do. Bluefyn analyzes transaction and provider data to classify and evidence each discrepancy; it does not move, hold, or custody funds.
The bottom line
Almost every PSP fee discrepancy is one of six things: a rate deviation, a fee overcharge, an FX markup, a missing fee, a duplicate fee, or a timing violation. The categories are not academic. Each one points to a typical cause and a specific piece of evidence, and together they turn the vague sense that provider charges are "a bit high" into a list of named, provable claims. The teams that recover the most are not the ones that suspect the most. They are the ones that can say exactly which of the six a charge is, and prove it.
Frequently asked questions
What are the main types of PSP fee discrepancies?
There are six: rate deviation (the wrong rate applied), fee overcharge (a discrete fee billed too high), FX markup (conversion margin above the contracted spread), missing fee (an omitted charge or, usually, a credit owed to you), duplicate fee (the same charge billed twice), and timing violation (a charge outside its contractual window). Almost every discrepancy a finance team finds is one of these.
What is a rate deviation?
A rate deviation is when a provider applies a different rate than the contract specifies for a transaction, such as charging 42 basis points where the contract sets 35. It is the most common discrepancy category and is often caused by tier misapplication, the wrong corridor rate, or a superseded contract version.
What is a duplicate fee?
A duplicate fee is the same charge billed more than once, for example a transaction charged twice, or a fee that appears on both an invoice and a settlement deduction. Duplicates are among the easiest discrepancies to recover because the evidence, two charges against one underlying event, is unambiguous.
What is a timing violation in PSP billing?
A timing violation is a charge raised outside the window the contract permits, such as a minimum monthly fee applied during a fee-free ramp period, or a fee billed in an excluded period. The amount may be correct, but the timing breaches a contract clause, so it only surfaces if the date is checked against the contract.
Is tier misapplication a separate discrepancy type?
No. Tier misapplication is a common cause, not a category. It typically shows up as a rate deviation or a fee overcharge, depending on whether it affects the rate applied or the amount of a discrete fee. The same is true of settlement deduction errors, which present as overcharges or duplicates.
Why does classifying discrepancies matter?
Because recovery depends on evidence, and each category names the specific evidence a provider will require to accept a dispute. Classifying a discrepancy lets a team attach the transaction, the contract clause, and the variance to it, turning a suspicion into a provable claim, and lets them see where their leakage concentrates.
