Payment Schemes Overview - StellarX402

A scheme is the contract between what a client authorizes and what a seller can charge. StellarX402 ships with two: exact and upto. A third, batch, is planned. Each scheme reuses the same verify/settle plumbing; the only thing that changes is how the amount is bound.

The schemes at a glance

Scheme	The client authorizes	The seller charges	Use when
`exact`	A fixed amount	Exactly that amount	The price is known before the work starts.
`upto`	A ceiling amount	Anything up to that ceiling	The final cost depends on the work (tokens processed, bytes returned, compute time).
`batch` (planned)	A rolling authorization	Aggregated across multiple calls	High-frequency callers with per-call amounts too small to settle individually.

How the scheme is negotiated

The seller declares which scheme applies in the PaymentRequirements that come back with the 402. The client cannot switch schemes unilaterally; if it disagrees, it simply does not pay. If a seller supports multiple schemes on the same endpoint, they can return an array of PaymentRequirements and let the client pick.

{
  "scheme": "exact",
  "network": "stellar:testnet",
  "amount": "10000",
  "asset": { "address": "C...", "decimals": 7 },
  "payTo": "G..."
}

Where next

Sellers: Choosing a Pricing Scheme.
Buyers: Budgets & the Upto Scheme.