Request credit paid by Pix: multipart with `usd`, `comprovante` (photo or PDF up to 2 MB) and `email`; the rest is optional.

The credit code comes back in the response and works once the owner checks the Pix and releases it (by hand, usually the same day). email is required: it is how the owner reaches the person. Optional: nome, pagina (the page the request came from, up to 2,000 characters) and what the person was buying when the 402 came — recurso (up to 2,000), descricao (up to 300) and preco_usd (decimal, e.g. 0.50); and navegador_id (a UUID that links the requests from the same browser). Everything that arrives is recorded with the request — the receipt included —, with the signed-in account (checked by the session cookie), the network and browser. Returns: { id, estado, credito, estado_em }