Why I can't sign into App Store or TestFlight with my Apple ID?

You can't sign into App Store or TestFlight as you might have Apple’s two-factor authentication enabled for your Apple ID.

Below are the steps to sign in to App Store or TestFlight with your Apple ID:

• Go to the App Store and click on the User Icon in the top right corner.
• Provide your Apple ID and Password.
• Enter the verification code for two-factor authentication and complete the sign-in process.
• Once you have signed in, search for and install your app on the App Store or navigate to the TestFlight App, and click Continue to proceed further.