Just for the record, LetsEncrypt is none of the things you are calling it (server, reverse proxy, etc.). It is a certificate authority (CA); signs certificate requests and issues certificates. The config you cited is that of an Nginx http server.
I know this post is old, but someone should have set the OP straight to begin with.
Reverse proxies, SSL termination, web servers, helm charts, integrations, batch files, anything having to do with installing Mayan.