As far as I can tell, I'm still on the original beta update (October 1st build date). When I go to Software Update -> Download and install it comes back with a November 1st build (G973U1UES2BSIV) which shows as an android 9 update. How do I get the beta update to come through instead of the android 9 one?
Go to Software info and find out what firmware you have. Beta 1 for unlocked device is ZSJA. if you are on ZSJA and registered (you should be registered otherwise you wouldnt be able to post here) I dont see why you are not receiving OTA.
if everything I mentioned above is right then Clear Cache of Software Update app from Settings -> Apps -> Show System Apps and clear cache of your Phone from recovery and retry.
If solution provided by @SlackingVeteran doesn’t help, please send us an error report with screenshots from One UI Beta App (Beta Feedback -> Send feedback-> Error Reports -> "Select Category" -> Input frequency and Description" -> Send (Top Right Icon). We appreciate your help for supporting beta program.
