Why can't I log into my Cash App account? When I submitted this question to Cash App's customer service, I did not receive an immediate response from a Cash App representative. In fact, they tell me that there are a number of reasons that can cause the Cash App login error. Bad internet connection, multiple logins to Cash App on multiple devices, and suspicious activity are some of the main reasons that can cause Cash App login errors. For smooth registration and payment, always make sure your internet connection is working properly. And always avoid multiple signups.