Whenever I try to open examples of ar.js online on my android phone.
https://stemkoski.github.io/AR-Examples/
I receive this message.
Usually, this error appears when the is a problem with the website SSL certificate or if you don't allow the website to access your phone's camera. In your case, it seems like you just need to give permissions to the website. You should also make sure your chrome version is up to date.