How to create a certificate for https connection

Hello everybody,

I’m curious how can I avoid next:

I’m using local machine with some local network IP. Should I use certbot instructions?
If yes, then does this clause in LoRa Server documentation is valid?
letsencrypt certonly --standalone -d DOMAINNAME.HERE
I’ve tried to google it, followed loooong instructions, but eventually still have this situation.

Thank you,
Oleg Somov