Hi @Klaus B.
Welcome to the Sonos Community!
Sorry to hear of the issue you’ve been having with installing the Sonos app.
First, can you please confirm that you are attempting to install the current (black icon) app from the Play Store and not trying to side-load a legacy version of the (gold icon) S2 app from earlier this year? I assume this is the case, but I just want to make sure.
If you have not already tried it, please reboot your phone.
Does your phone have plenty of storage space left? Do you get any error messages when trying to install the Sonos app?
Could you please post some screenshots of the process going wrong? Thanks.