Yes, I have uninstalled monica, restarted the server to be on the safe side, and then tried reinstalling monica.
The output was:
Linux my-server 4.9.35-v7+ #1014 SMP Fri Jun 30 14:47:43 BST 2017 armv7l GNU/Linux
So im on Raspbian GNU/Linux 8.0 (jessie).
Can I install PHP7.1 by hand before monica or may it cause more problems?