Execute a currency conversion between two of your accounts.

Two execution modes:

1. With Quote ID (recommended):

   • First obtain a quote using POST /conversions/quotes
   • Execute using the quoteId to lock in the quoted rate

2. Without Quote ID:

   • Provide fromAccount, toAccount, and amount directly
   • A quote will be created and executed immediately at the current market rate

Quote-based execution is recommended for predictable rates, especially for large amounts.

Instruction Type: Use instructionType to control whether the amount represents the source or destination side:

• sell (default): The amount is the source amount you are selling
• buy: The amount is the destination amount you want to buy