iTunes Store Sandbox Account Authentication Error: 'No auth plugin to verify credentials'

This error message indicates that there is no authentication plugin available to verify credentials for iTunes Store sandbox accounts.

To resolve this issue, you can try the following steps:

Check your device's internet connectivity: Ensure that your device has a stable internet connection.
Sign out and sign in again: Go to the 'Settings' app on your device, then select 'iTunes & App Store' and tap on your Apple ID. Choose 'Sign Out' and then sign in again with your iTunes Store sandbox account.
Reset your device's network settings: In the 'Settings' app, go to 'General' > 'Reset' > 'Reset Network Settings'. This will remove all saved Wi-Fi networks and their passwords, so make sure you have them handy.
Update your device's software: Make sure your device is running the latest version of iOS or macOS. Go to 'Settings' > 'General' > 'Software Update' to check for any available updates.
Contact Apple Support: If the issue persists, it may be necessary to contact Apple Support for further assistance. They can provide more specific troubleshooting steps or investigate if there is a problem with your iTunes Store sandbox account.

Remember that iTunes Store sandbox accounts are used for testing purposes and may have limitations or specific requirements.