Nginx Proxy Manager - Port in use error/web UI not launching

Failed to start addon
Port ‘80’ is already in use by something else on the host.

Just installed and this popup shows when I try to run. After setting it to any other port, the web UI still doesn’t launch. Unsure what to do here.

I am using DuckDNS with HA Supervised.

It’s only say that port 80 is in use. You have to check what is using port 80.