Bitrefill x402 Invoice Payment

Use this endpoint as the final payment step after creating an invoice via the Bitrefill x402 invoice creation endpoint. This is the only endpoint that actually executes and settles the USDC payment on-chain. Use it when you have a valid invoice_id and are ready to commit the purchase — not for browsing products, checking prices, or creating invoices.

• Invoice not found or invalid invoice_id — returns error with unknown invoice
• Invoice already paid — returns error indicating duplicate payment attempt
• Insufficient USDC balance or payment amount mismatch — payment rejected
• On-chain transaction failure or revert — network error response
• Invoice expired or price-lock lapsed — requires new invoice creation