This method searches Omneo for existing transactions, if found the payload is used to update the existing transaction. If no transactions are found, a new transaction is created instead.

The search for a existing transaction first looks for a transaction with a matching external_id
If one is found, the transaction is updated.

If the external_id is not provided, or not found in Omneo, the search will look for a transaction matching the id parameter provided. If a matching transaction is found, the payload will be used to update the existing transaction.

If no transactions are found with a matching external_id or id a new transaction is created.

This method is often preferable if a reliable external_id or id can be provided to Omneo during the creation. This saves the need to call the Add Transaction and Edit Transaction separately.