How to handle net::err_failed?

Question

Java

Greetings. There is an application on WebView and I would like to open some other window if the user tries to open the page, but he does not have an Internet connection.
And now I have such a krakazyabra displayed.

I tried to google the net::err_failed event. I did not find anything understandable for myself

PS do not judge strictly - I'm a

PS2 teapot. there is a nuance - the site being opened is on pwa, and some pages are opened offline