Ive been running Beta 3 on one of my test devices for two weeks now.
I noticed Beta 4 came out yesterday, but Im not getting any OTA update, and when I attempt to restore from inside itunes, I get told my device is inelegible for the requested build.
What gives?
Delete any profiles in Settings > General > Profiles. Restart your iDevice, and try again. The Apple Watch profile has blocked OTA updates for quite a few people - You may need to restart more than once.
Obviously, if you have an Apple Watch, then you can just reinstall the Watch profile as you did before after the update.
If the above doesn't help, the Apple support page for the error you're getting from iTunes is here: