Stripe Connect for MCP servers: what we learned building it

Shipping the Monetize tier for Cognoverge — where MCP server authors can charge per tool call — was easier and harder than we expected. Easier because Stripe Connect is genuinely a well-designed product; harder because "marketplace billing for tool calls" hits edge cases that Stripe's API assumes away.

Here's what we learned building it — the six things that killed a weekend, and the design choices we'd make again.

1. Meter first, charge later (much later)

A tool call happens in ~200ms. Charging Stripe on every call is infeasible — Stripe's minimum transaction is $0.50 and the API overhead is 250ms per charge. We batch every caller's tool calls over their billing cycle and issue one metered charge at the end. This means we run our own metering ledger with strong durability guarantees. Skip this and you'll owe your customers refunds.

2. Tax is more complicated than payments

Stripe Tax computes sales tax and VAT at checkout, which is table stakes. What surprised us: India GST. If you're selling to callers outside India from an Indian entity, GST is zero (export of service) — but only if you can document the caller's location. So we now capture and retain that per-charge, per-caller.

3. Refunds propagate weirdly

When a caller disputes a charge, Stripe pulls back the full amount including the platform fee. If we've already paid the server author their 95% cut, we're out of pocket. We now hold a rolling reserve on newer accounts and settle net at each payout.

4. Onboarding is the hardest part of the whole feature

Stripe Connect Express onboarding is a beautifully-designed flow. It is also a flow that requires an Indian developer selling a Notion MCP server to fill out an American EIN or a UK bank routing number depending on where they clicked the wrong link. We wrote a pre-onboarding wizard that pre-fills Stripe based on the CLI user's workspace region, and the completion rate went from 41% to 84%.

5. Currency conversion happens twice

Caller in Germany, MCP author in India. Caller pays in EUR. Stripe settles to USD on our platform account. We pay out to INR. Each conversion has a small spread. We now show authors the effective rate on every payout so it's not a mystery.

6. Payouts must be predictable, not just fast

We considered daily payouts. Then we talked to a dozen MCP authors — they wanted weekly. The variance from daily payouts made bookkeeping annoying and gave everyone anxiety. Weekly Monday payouts, always the same day. Predictable beats fast.