Accepts an active quote identified by its UUID.

FX Quote acceptance:
Verifies sufficient balance, then executes a two-leg simulated trade (source → USDC → target) using amounts locked at creation time. All operations run inside a single database transaction.

Payout acceptance:

1. Validates the quote has not expired.
2. Encodes and submits beneficiary requirements.
3. Creates and signs the payment transaction.
4. Submits the transaction for settlement.

After payout acceptance, the payment transitions to processing status. Once settled, it will be marked as completed or failed.

Returns 422 if the quote has expired or if there are provider/balance errors.