Payment facilitator vs ISO — what's the difference?
The terms 'payment facilitator', 'PayFac', 'ISO', 'sub-ISO' and 'merchant aggregator' get used loosely in UK payments — sometimes interchangeably, often wrongly. The differences matter because they determine the regulatory weight you carry, the capital you need, the economics you earn and the customers you can serve. This guide pulls them apart in plain English.
The simplest version of the difference
An ISO refers merchants to a regulated acquirer. The acquirer holds the bank licence, the card-scheme membership and the merchant agreement; the ISO is paid a residual for the introduction.
A payment facilitator (PayFac) holds its own sub-merchant agreements and processes payments on behalf of those sub-merchants under its own contract with the card schemes — sitting between the acquirer and the merchant, taking on regulatory and capital weight that an ISO does not.
Said simply: an ISO is a referral relationship. A PayFac is a regulated counterparty.
What an ISO actually does
An ISO (Independent Sales Organisation, sometimes called a Member Service Provider or MSP) sources merchants, helps them apply for an acquirer-issued MID, and earns a residual on the processing volume that follows. The merchant signs a contract directly with the acquirer; the ISO is paid by the acquirer.
The capital requirement to operate as an ISO in the UK is effectively nil — beyond the working capital to fund the sales motion. The regulatory weight is light: the FCA does not authorise ISOs directly, though some acquirers ask for AML and CFT screening before approving an ISO relationship.
Economically, the ISO's upside is the residual share negotiated with the acquirer — typically 50-80% of the acquirer's margin on the merchant's processing, depending on the relationship and the value the ISO adds (statement analysis, support, retention).
What a payment facilitator actually does
A payment facilitator holds its own sponsorship agreement with a scheme-member acquirer and onboards merchants as sub-merchants under that agreement. The PayFac becomes the merchant's counterparty for the card payments, settles funds to the merchant directly, and carries the underwriting and chargeback risk that would otherwise sit with the acquirer.
Examples of PayFacs operating in the UK include Stripe, Square, Sumup, Zettle, and a long tail of vertical-specific platforms (Toast for hospitality, Mindbody for fitness, etc.). Each one took on the regulatory and operational weight of being the sub-merchant counterparty in exchange for the ability to onboard merchants in minutes rather than days.
The capital and regulatory requirements are non-trivial: scheme sponsorship, AML/CFT programmes, chargeback reserves, ongoing underwriting, and compliance with each card scheme's PayFac rules. Building a PayFac from scratch is a multi-million-pound undertaking; most teams that want PayFac-shaped economics white-label off a PayFac-as-a-service provider instead.
When each model fits
The ISO model fits when the customer is a traditional SME merchant who needs a card terminal or a gateway, the sales motion is consultative (statement analysis, contract reviews, residual saves) and the team's strength is in field sales and account management.
The PayFac model fits when the customer is a software platform's user (SaaS company, marketplace, vertical platform) who wants payments embedded in the product without a separate underwriting step. The economics are higher per merchant but the capital, compliance and operational burden are vastly heavier.
Most UK consultancies and field sales teams in merchant services are ISOs and will stay that way — the ISO economics are excellent if the portfolio is grown and retained well. PayFac is a different business with a different customer.
Sub-ISO, master ISO and aggregator — the inside-the-channel words
Inside the ISO world there's another layer of vocabulary worth knowing. A master ISO is an ISO with the contractual right to recruit and pay sub-ISOs — effectively running an ISO programme of their own. A sub-ISO is an agent who works under a master ISO rather than directly with the acquirer, in exchange for the master ISO's training, tooling and acquirer access.
An aggregator is a slightly older term that overlapped with what we now call a PayFac — historically used for processors that batched many small merchants under a single MID. Modern usage usually points to the PayFac model.
Most new entrants to the UK merchant services channel start as sub-ISOs under a master ISO, build a personal book, and either stay sub-ISO indefinitely or graduate to direct ISO status with one or more acquirers. The cornerstone guide to becoming an ISO agent in the UK walks through that journey in detail.
Regulatory and tax implications
ISO agents in the UK are normally self-employed or operate through a limited company. Residual income is treated as ordinary trading income for tax purposes, with the usual VAT treatment (residuals between UK businesses are generally outside the scope of VAT, but specifics vary — get accountancy advice).
PayFacs in the UK operate as either authorised payment institutions (APIs) or e-money institutions (EMIs) under FCA rules, depending on the model, with the capital requirements, safeguarding obligations and reporting that those statuses require.
For an ISO, the regulatory surface is light. For a PayFac, it is the centre of the business.
Frequently asked questions
What's the difference between an ISO and a payment facilitator?
An ISO refers merchants to a regulated acquirer who holds the merchant agreement and pays the ISO a residual. A payment facilitator (PayFac) holds its own sponsorship agreement and onboards merchants as sub-merchants under its own contract — taking on the regulatory, capital and chargeback weight that the acquirer would otherwise carry. ISOs introduce; PayFacs underwrite.
Is Stripe an ISO or a payment facilitator?
Stripe is a payment facilitator. It holds its own scheme sponsorship and onboards customers as sub-merchants under that sponsorship, which is why Stripe accounts open in minutes rather than days.
Can I start as an ISO and graduate to a PayFac?
In principle yes, but the gap is large. The capital, compliance and operational requirements of running a PayFac are an order of magnitude beyond running an ISO programme. Most teams that want PayFac-shaped economics white-label off a PayFac-as-a-service provider rather than building from scratch.
Which is more profitable per merchant?
PayFac economics are typically higher per merchant — often 1.5-2x the per-merchant residual of an ISO arrangement on the same processing volume — in exchange for taking on chargeback risk, capital requirements and ongoing regulatory burden. The ISO model has lower per-merchant economics but vastly lower fixed cost and risk.