These are just a few steps to troubleshoot this issue:
Is your clients using the MyCoach or your personalized Branded App? I occasionally see clients try to use the Coach Catalyst app, this is for coaches only. 😊
Check to make sure the email address they are using has no spaces/ or capitals. Sometimes the space will be after the email address, it's always worth checking.
Are they using the password they got in the email or a password? I suggest sharing their app code which is in the client's dashboard. This is a six-digit numerical code that will work for the password.
If this is still an issue please message us in support or email: firstname.lastname@example.org and we will get this working for you.