Nginx and NPM (NPM does not work)

With docker-compose.yml I created a container where nginx proxy manager runs on the dashboard.
On the same host machine there is already Ubuntu installed with another classic nginx container which works correctly with the various settings and the various.conf files and the redirection from the different domains to the local machines is ok.
I then installed npm with this docker-compose (I set 8081 for host because port 80 is already used by classic nginx), I access the dashboard from but when I add a host proxy it is as if I did not add anything and the redirection does not works.

Am I wrong because it could never work because there is already classic nginx or am I missing something?

version: ‘3.8’
image: ‘jc21/nginx-proxy-manager:latest’
reboot: unless interrupted
- ./data:/data
- ./letsencrypt:/etc/letsencryp

I hope someone can help me, thank you very much