In the section Declines in your Payyo Backoffice you can find the reason why a transaction was declined. The great filter option will help you to find the declined transaction you are looking for.
There are many reasons why card schemes refuse a transaction. The corresponding authorization responses we receive are not the same for all schemes and change from time to time.
Here is an overview of general raw acquirer responses to refused and cancelled transactions that might help you to understand the problem: https://developers.payyo.ch/error-codes