Vaultwarden in https behind Nginx Proxy Manager

Hello,

I have vaultwarden installed in docker image and Nginx Proxy Manager (NPM) in another docker image on my QNAP TS-673A. The vaultwarden has the ip 192.168.0.227

NPM listens on this two ports :

35443
35080

On my router the port 443 and 80 are already used by others services, so i have set up :

on my router 16897 forward to 35443 on the ip 192.168.0.228 on my NAS

I can access to http://192.168.0.227 but not to https://192.168.0.227

In NPM i have set up the proxy with the domain https://pass.mydomain.com, when i try https://pass.mydomain.com:16897 i have the let’s encrypt certificate but i have an error page : 502 Bad Gateway

What i have missed in the configuration ?

Thanks by advance