Apple Configurator sign in problems

Currently, I'm testing adding a Mac device to Apple Business Essentials via Apple Configurator with the help of an iPhone.

I've created a managed Apple ID + prepared my iPhone with iOS15. I've downloaded the app "Apple Configurator" from Apple Store and installed it. Within my first test, I was able to sign in with the managed Apple ID to Apple Configurator and I could successfully add a Mac Mini device to Apple Business Essentials.

I released/removed the device on purpose from Apple Business Essentials to add it again via Apple Configurator for another test scenario. This time, I was not able to sign in with my managed Apple Id to Apple Configurator. Suddenly, I was asked if I want to use the personal Apple ID "xyz" for iCloud (see screenshot below). I tried every possibility but ended up with errors all the time. So, I'm not able to use Apple Configurator for adding a Mac device to Apple Business Essentials anymore.

As an information, I did not change any configurations in Apple Business Essentials in between these two tests.

Can you help me? Has anyone experienced the same scenario?

Thanks for you help!