Process a transaction

Create a composite transaction that may include multiple line items and payment methods.
The response will contain the transaction status, including points earned, points redeemed, and
the customer's points balance before and after the transaction.
In case of a failed transaction, an error message will be returned.
Transactions are processed asynchronously, and the status can be checked later using the URL provided in the response.
The request accepts either a customer ID or a customer barcode. You can pass a unique ID for the transaction, or one will be generated automatically if not provided.
To simulate a transaction without processing it, set the 'simulate' query parameter to 'true'.