Sent as X-API-Key header
X-API-Key
btq-service base URL (without /payment-invoices)
/payment-invoices
return_url — customer is redirected here after payment (optional)
return_url
callback_url — webhook with the payment status
callback_url
International format (E.164), e.g. +905321112233
+905321112233
user_id — must be a UUID. Auto-generated if empty.
user_id
click_id — auto-generated if empty
click_id