Hello Robin,
we are now back on the WebConf but have the condition that our previous sites are not displayed.
When downloading CheckMK version 2.2.0p25 for the appliance with firmware 1.7.0 we get the file “check-mk-enterprise-2.2.0p25-3-x86_64.cma”.
During upload and installation, however, we are told that this version is not compatible with 1.7.0.
What are we doing wrong?
The 1.7.0 enterprise file should have number 4 inside.
https://download.checkmk.com/checkmk/2.2.0p25/check-mk-enterprise-2.2.0p25-4-x86_64.cma
As said most times i would not recommend the selection process inside the web gui.
Better it to use the “Download archive” button. 
I checked the download link after the selection process and it gives the wrong file back. That is something for the web server team of CMK to fix.
I had already thought that this identifier -3- or, as in this case, -4- in the file name indicates compatibility to the system. However, I have always been offered the -3- in the download portal.
After uploading the setup data, there was no more message and I was able to install it and successfully update and start my sites.
Many thanks to all.