Can't save FormBuilder Form Fields

I’m using the awesome FormBuilder Plugin like I use it in almost of all my projects. But now somehow I can’t save the Form Fields. I tried it on a blank Kirby Installation and on my live server but the error occurs everywhere :bowing_man:‍♂

Any help debugging the problem?
Thank you

I think that’s related to this issue:

Downgrading to 3.4.2 should fix it.

Ah nice, it’s working now. Thanks!