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 before expiresAt. After expiresAt, execution is rejected
   • executable: settles at the quoted rate
   • indicative: the sell amount is fixed. The buy amount may differ from the quote, including before expiresAt

2. Without Quote ID:

   • Provide fromAccount, toAccount, and amount directly
   • A quote is created and executed immediately. The same executable or indicative rules apply

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