Actually, at the time of using the Cash app account, you may experience that whenever you make any transaction or make any changes, then it asks you to enter your last four digits of SSN. SSN is social security number created by the user itself to secure an account. So, if you didn’t remember your SSN then it is obvious that you will get an issue Cash app won't let me send money. And, if you have still any issues, then dial this below number to contact our support team.