I am not an NPM expert but it looks like you now have to do that.
I see you got a cert (two, actually) so now you just have to configure your system for HTTPS and to use that cert. We focus on helping people get certs. We also often help configure common servers. But, NPM is a configurator that is hard to debug. Their support is the best place to resolve this. I saw other people posting about the same problem on their github.
If you can't resolve it you might want to reconsider using NPM. If you just want to run a webserver you might try running nginx by itself without NPM and containers. In the end you need a system that you can manage and understand.