First, make sure you are logging into your Admin site and not your Users site as this is a common mistake.
The Admin login will be similar to: https://organizationname.reachapp.co/admins/sign_in whereas the Users/Supporters login will be similar to: https://organizationname.reachapp.co/users/sign_in.
If you are still having trouble, try to reset your password by clicking on the 'Forgot Password' link.
Still having trouble? Email us at firstname.lastname@example.org.