- source asset and chain, or source fiat;
- exact-source or exact-destination mode;
- amount;
- destination asset or fiat currency;
- destination country;
- optional routing preference.
recipient_requirements to ask the user which instrument to use
and collect only that instrument’s required fields before creation.
If no live route exists, explain that it is currently unavailable. Do not
invent a corridor, split the payment, or silently change chains.
