I have tried to use BEAMER_FRAME_LEVEL instead of setting specific
sections/environments for the individual levels. If I remove all
entries from the sectioning part of org-export-latex-classes, `nil' is
called as a function. If I put anything in the sectioning part of
org-export-latex-classes those commands are used no matter what I set
as BEAMER_FRAME_LEVEL.

I'd like to use BEAMER_FRAME_LEVEL. How to do it properly?

Thanks and best regards,

Marko