In the meantime, I have become smarter myself. With *#1234# you can find out the exact version of the phone. Under CSC, a country code is entered in positions 6-8. In my device, DBT stands for Germany (branding-free). The Swiss code (branding-free) would be AUT.
It is not nice that Samsung ties the functionality of its phones to these country codes, probably also wants to protect its official distributors and make business more difficult for companies like Digitec. I expect more proactive communication from Digitec on this vexed issue.

I bought the S7 about 2 years ago and it worked without any problems.

It also worked for me without any problems.
I bought my S7 about 2 years ago.

Is it possible that Samsung Pay does not work because it is an EU version of the S7? It would be fair if digitec would note that and not just point out the lack of VoLTE and WiFi calling!