Introduction

Operation currency is USD by default. Settlement follows the shop balance model. The `amount` you send is in USD major units unless you pass a `currency`. Optionally you can initiate in a PRESENTMENT currency (`currency: "EUR"`, `"MXN"`, …): we convert `amount` (in that currency) to a USD headline at our rate minus the FX markup. Ledger credits and settlement follow the shop balance model (USD or local currency). In the RESPONSE your presentment values come back as `inputCurrency` + `inputAmount`, and `currency` is ALWAYS `"USD"` (the converted USD is `amount`). New fractional requests round upward before FX. When presentment matches the rail currency, the accepted amount is the local request; otherwise it is converted once at creation. `amountLocal` + `currencyLocal` describe the local request, with exact provider-calculated amounts preserved.

USD-model shops accept USD or supported local-currency requests and are credited in USD. Local Currency shops require the country's enabled native currency: MXN for Mexico, BRL for Brazil, USD for Ecuador. A different currency is rejected. Local principal stays in that currency without entry FX markup; converting available funds to USD is a separate quoted swap. Each provider's currency contract is preserved, including a provider-fixed USD amount when applicable.