Error code U13 in Google Pay indicates that the application encountered an issue when attempting to communicate with the bank servers. This error occurs when Google Pay is unable to connect to the bank server, which can happen if the bank server is down or if there is an issue with the internet connection. The only solution for this error is to wait and try again later. If the issue persists, users can visit the Google Pay Help Center or select from the Google Pay "Need Help?" menu to get assistance.