I am not able to sign-in to App Store or TestFlight with my Apple ID. How can I fix it?
Open the App Store & Click on the Blue User icon on the top right corner of the App Store Home Page.
Enter your Apple ID and Password.
Enter the verification code when prompted and complete the sign-in.
Once signed-in, you can search for and install your desired app on the App Store.
OR open the Testflight App, and click ‘Continue’ to view and test your iOS Apps.