How to add marketplace payments to an existing app
How to add marketplace payments to an existing app: the payment models, six build steps, and Stripe Connect, Fynex, Adyen, PayPal and Mangopay compared.
The easiest way to add marketplace payments to an existing app is to keep the checkout you already have and add the marketplace half on top: seller onboarding, the split between your commission and each seller, payouts and reconciliation. The alternative is to rebuild payments on a platform-payments toolkit such as Stripe Connect, which gives you the parts and leaves the assembly to your engineers.
This guide covers the three payment models a marketplace can run on, the six steps to add marketplace payments to an app that already takes money, and how the main options compare on cost, sellers per order and reconciliation.
The three ways a marketplace can take payments
A marketplace takes payments in one of three ways: as a platform on a provider’s accounts, through a provider acting as Merchant of Record, or as a payment facilitator in its own right. The choice decides who carries chargebacks and tax, and how much of the flow you build.
| Model | Who carries chargebacks and tax | What you build | Fits |
|---|---|---|---|
| Platform on a provider (Stripe Connect, Adyen for Platforms) | You, as the platform | Onboarding flow, split logic, payout handling | Most marketplaces with engineering capacity |
| Split and payout layer on your existing processor (Fynex) | Shared, and Fynex can act as Merchant of Record | Configuration: split rules, payout schedules | Apps that already take payments and want to add sellers |
| Your own payment facilitator | You, fully | Underwriting, risk, compliance, the lot | Very large volume only |
The difference between the last two is covered in merchant of record vs payment facilitator.
How to add marketplace payments to an existing app, step by step
Adding marketplace payments means adding five things your app doesn’t do yet: knowing who each seller is, dividing each payment, holding money until it’s earned, paying sellers out, and matching every payout back to the order.
- Pick the model. Platform on a provider, a layer on your existing processor, or your own payfac (see above). This decides everything below.
- Onboard sellers with KYC and KYB. Every seller is verified before they’re paid: individuals with KYC, companies with KYB. Do it inside your own signup so sellers don’t drop out. See seller onboarding.
- Define the split. Your commission, each seller’s share and any partner cut, per seller where terms differ. Keep it in configuration, not code, so a renegotiated rate isn’t a release. How split rules work.
- Decide when funds release. On delivery, after a dispute window, or after a fixed number of days. See escrow and held funds.
- Pay sellers out. On a payout schedule or on demand, in each seller’s currency, over the cheapest rail that reaches them.
- Reconcile. Every payout, fee and refund posts back to the order it came from, in your accounting system.
Test the whole cycle, from one order to a split to payouts to the books, in a sandbox before switching it on.
The best payment solution for a two-sided marketplace
The best payment solution for a two-sided marketplace is the one that matches how many sellers share an order, where your sellers are, and how often your commission terms change. The main options:
| Sellers per order | Split logic | Payout rails | Reconciliation | Platform-layer cost | |
|---|---|---|---|---|---|
| Stripe Connect | One (destination charges) or several (separate charges and transfers) | Application fee or transfers you compute | Stripe payouts | Stripe reports; you match transfers to orders | $2 per monthly active account + 0.25% + 25¢ per payout (US) |
| Fynex | Several, plus partners and fees | A versioned rule per seller, edited from the dashboard | The cheapest compliant rail per seller | Every leg posted back to the order in Xero or QuickBooks | Cards from 1.4% + $0.20/auth; payouts 0.5% (min $1) + $100/mo |
| Adyen for Platforms | Several balance accounts | Split instructions at authorization or capture | Adyen payouts | Adyen reports | Contract pricing |
| PayPal (multiparty) | One or several | Platform fees on PayPal orders | PayPal balances and bank transfers | PayPal reports | Published PayPal rates |
| Mangopay | Several e-wallets | Transfers between wallets | Bank payouts | Provider reports | Contract pricing |
Sources:
- Stripe: its charge-type guide says destination charges suit “a single connected account”, and that separate charges and transfers, the multi-seller option, “require a more complex Connect integration”. The Stripe costs are from Stripe Connect pricing, for the plan where the platform sets its own prices.
- Adyen: its splits are described in Adyen’s split transactions docs.
- Card processing: every figure above is on top of card processing.
The deeper comparison is in Fynex vs Stripe Connect.
What payment solutions do top marketplaces and platforms use?
Many of the best-known marketplaces run on Stripe Connect. Stripe’s own documentation uses these examples:
- Shopify for direct charges
- DoorDash for splitting one payment between several parties
- Airbnb and Lyft for Express connected accounts
That tells you Connect scales. It also tells you those companies have payments engineering teams to build and run the flow.
A marketplace without that team usually wants the opposite trade: fewer parts to assemble, and rules that live in a dashboard rather than a codebase.
What it costs, worked through
Take a marketplace with 200 active sellers, 800 seller payouts a month of $500 each, and $400,000 moving through it.
- Stripe Connect (platform-set pricing): 200 × $2 = $400 in account fees, plus 800 × (0.25% × $500 + $0.25) = $1,200 in payout fees. That’s $1,600 a month in the platform layer.
- Fynex: no account fee; 800 × (0.5% × $500) = $2,000 in payout fees, plus the $100 payouts plan. That’s $2,100 a month in the payout layer.
Card acceptance sits outside both lines: Stripe bills its processing on top of Connect, and Fynex’s is 1.4% per payment on US-issued cards plus $0.20 per authorization (pricing). Run your own split in the split payment calculator.
The compliance you take on
Adding sellers means adding verification and tax reporting.
- KYC and KYB. Every seller is verified before payout; businesses need their controllers identified. See KYB.
- Form 1099-K (US). A payment settlement entity files Form 1099-K for a payee only when their gross payments exceed $20,000 and their transactions exceed 200, the threshold restored by the One, Big, Beautiful Bill (IRS). Who files depends on your model.
- Held funds. Money you hold between buyer and seller is client money. It must sit safeguarded, not in your operating account.
Where Fynex fits
Fynex adds the marketplace half to an app that already takes payments. Sellers are onboarded with KYC and KYB inside your signup. Each payment is split by a per-seller rule, held until your release condition, and paid out over the cheapest compliant rail in the seller’s currency. Every leg is reconciled back to the order in Xero or QuickBooks. Your checkout, and the processor behind it, stay where they are. See Fynex for marketplaces.
Related: multi-party payments from one checkout · how to pay out marketplace sellers · how to hold funds in a marketplace · split payment calculator