This massage get when put on install ios 15 which downloaded from phone yesterday,(an error occurred installing ios 15) unable to install update

Assuming you're trying to update your device wirelessly (via wifi), see this suppport article:--> If your iPhone, iPad or iPod touch won’t update

If the issue persists, try to update it via computer:

Learn how to update your device manually if you're using a Mac with macOS Catalina or later, or if you're using a Mac with macOS Mojave or earlier or a Windows PC.

If you still get no help, contact Apple Support directly, using this link:--> Get Support

Regards

Giulio

We had the same problem. Tried all the suggestions and nothing worked. We had to fully delete our VPN app and then the update worked.