There might be times when you might have trouble to activate Cash App card due to error while launching the app. In such an event, you can try rebooting the device to start the app or you can dial the assistance number and get in touch with the customer care to seek his help in dealing with the issue.
https://www.gonetech.net/cash-app-customer-service/
https://www.gonetech.net/cash-app-customer-service/