You can use the Execute Transaction form for debugging purposes. NOTE: If a transaction is successful, it does create the record(s) in GP. This is available in both ExpenseConnect & InvoiceConnect and can be used for Expense Reports, Payment Requests, and Payment Confirmations.
Open the ReportDetails.xml for the report that you are working with. Then, copy the text starting from the line starting with "<taPMTransactionType..." to the second-to-last line at the bottom of the .xml which should say "</taPMTransactionType>".
Then, be sure to change the voucher number (<VCHRNMBR>) or other information for testing as needed. Then click "Process" and it will try to create that voucher within GP. If it went through successfully and created a voucher, then the Result message will say "Success". If it did not go through successfully, then in the text box underneath the Result message, it will list out the error message(s).