Skerry/ Reference/ Paying by the call

Paying by the call9

Price a resource and let automated clients pay for each call. Skerry builds the 402 for the customer's server in both x402 and the Machine Payments Protocol, checks the payment the client sends back, and settles it on the customer's own merchant account. Skerry runs no facilitator and holds no keys. A preview: every call answers 409 capability_coming_soon until it is switched on for the customer.