How do I view declined transactions and their error messages?

To view declined transactions and the error message, download the Transactions export (Analytics --> Exports).

Once downloaded, you can use the "type" column to remove all transactions except for purchases and then use the "status" column to filter out everything except for declines.

Once you have done that, you can use the "gateway_error_codes" column to determine why the transaction declined.

Please keep in mind that gateway error codes will vary depending on the payment gateway you are using, so you may need to lookup the error code on the gateway's website to get more details about the decline.