Unified - HTTP Request was send to HTTPS Port

i tried Bitwarden Unified on my Synology. I can connect to it but everytime I tried something like send an E-Mail to verify the account or add a Item i get a Error “400 Bad request. The plain HTTP request was send to HTTPS Port”.
The Connection is via the Build-In Reverse Proxy from Synology. The Settings see the Image below.

Have anybody an Idea, what I can do?