I'd be glad to help you with logging in to your QuickBooks using the mobile app.
It could be that you've incorrectly entered your login credentials. The email address and password are case sensitive. You may want to retype the information and make sure it's correct. If you're still unable to log in, you may consider resetting your password. I'll show you how:
From the sign-in page, select I forgot my user ID or Password.
Enter your email address or phone number and select Continue.