Problems setting up second proxy manager on nc host

i strucle with the setup of “local proxy manager in the middle”.
has anyone a setup guide for this advice from Nextcloud doc?

i have already a reverse proxy for all my servers, running fine.
But for nextcloud i need an extra reverse proxy on the nextcloud server.
i installed nextcloud via portainer an can access the ui (without proxy manager config). then i changed nc config for using reverse proxy and install a second nginx proxy manager via portainer on the same machine.
my understandig is, that i have to configure it to access https requests an send this withous ssl as plain http to my nextcloud (so if i use the url from proxymanager without ssl i should also access the nc instance?)
i setup a “listen” domain with the ip-adress and send it to the same ip-adress on port 11000. but get BAD GATEWAY

Advice: If you need https between Nextcloud and the reverse proxy because it is running on a different server in the same network, simply add another reverse proxy to the chain that runs on the same server like AIO and takes care of https proxying (most likely via self-signed cert).