Problem installing chat relay [certificate for shared IPv4 address space]

I forgot to mention. I’m trying to install to a Raspberry Pi behind a fritzbox. My local machine is in the same intranet. Ports a forwarded as seen in the picture. The output of netstat executed on the Rasp is as following:

edit: I can also use a certificate from strato instead of the lets-encrypt-cert

Output-netstat-nltp.txt (1.9 KB)