What do you obtain? A copy of the error message or a screenshot is always useful.
When in full-screen mode, if back button is pressed, the app directly minimizes.
When does this occur?
Press back button
What should be the behaviour from your point of view? How do you expect the service to work?
The expected behavior should be just to exit to the full-screen mode. Now, this can be implemented 2 ways:

OR

Which one should I go with? @mhutti1 @srv-twry Open to your reviews. Others can say their minds as well.
IMO we should go with the second one i.e. go to the parent webview before exiting the full screen mode.
Reason: If we go for the first one, then we won't have any way to go back to the previous webview without leaving full screen. In that case the user would have to leave full screen first, go back to previous web view and then enter full screen again.
While in the second option, if he/she wants to stay at the current screen and only leave full screen, the exit full screen button can be used.
Seems fair ?
@srv-twry Sounds logical to me. I'll wait for @mhutti1's view, although I think even he will go with the second one.
I too think that the second approach is better.
Yeah second sounds better.