Many people have recently had trouble logging into the Starbucks app. Deleting the Starbucks app and then reinstalling it has been known to solve the login problem.
Note: If you tried multiple incorrect passwords to access the app, you may be locked out. According to Starbucks customer service, there is a 24-hour lockout period although the app will not give you any indication you’re locked out. However, reinstalling the app is the best way to ensure best results.
If you’re on a smartphone and login to the Starbucks website, it’s possible to use the mobile version of the website to make purchases using your Starbucks card. It’s also a way to confirm that your username and password are working correctly.
If this works for you, or doesn’t, feel free to post your experience in the comments below.
Thanks!
Iowa City Technology Services 
It won’t let me sign on Starbucks app or web page