405 Not Allowed (nginx) when doing "POST" for SAML

I get a “405” from nginx when I try to login to sogo using SAML.
weird enough this only happens on my 2nd mailcow.. on the first it works. so there needs to be a difference there (both have the latest version, but one of them (not working) was freshly setup and the other one is a few months old (working).

till now I only found a difference in “redirect.conf”. the new one contains

  location ^~ /.well-known/acme-challenge/ {

the old one does not.