K-9 mail keeps stopping

I tried to (re)install K-9 mail several times from apps. Every time I try to open it stops.
Anyone suggestions why.

I forgot to mention that the initial setup of my email-adress worked fine. After that K-9 mail stoppes if I try to fetch my mail.

My K-9 worked fine when I had it, but I got it from F-Droid rather than Apps, not sure if that made a difference. Not using K-9 anymore, as I’ve switched to SimpleEmail.