I had to install this pem (downloading, changing extension and passing through bluetooth) https://letsencrypt.org/certs/isrgrootx1.pem.txt
This chinese ROM does not allow to install in Android OS Settings > Security > Install Certificates From Storage as per the website instructions, but you can install in Android OS > Options> WLAN> Additional Options, and then instead for WLAN select something like VPN and Apps.
It did the trick, and it does work now. Thank you.