Ah I think I got it. this is wrong:
* mentaljam-obs … [Index of /obs/home:/mentaljam/4.3.0.15_armv7hl](http://repo.merproject.org/obs/home:/mentaljam/4.3.0.15_armv7hl/)
Anyway you should be able to
devel-su ssu rr mentaljam-obs
pkcon refresh
and things should start to work again.
Later you can do
ssu ar mentaljam-obs http://repo.merproject.org/obs/home:/mentaljam/4.3.0.15_armv7hl/
taking care that it’s a proper URL.
But it would be interesting how this ended up in your repo list. Did you ever add that repo manually? It looks like it can be caused by copy-pasting from this forum or another place which silently replaces URLs by markdown syntax.