ProSites (Supporter) Settings Will Not Save

Hi -

I am unable to update any of the settings (Prosites > settings > general settings). I am running the most recent Prosites (3.0) but had this issue on the previous version (although I know this is a user error, I just can't figure out what the issue is).

This is true of all settings on this page, here are two examples:

+ Free trial settings will save, show that they are saved, but will not "take" and when I log out and back in to settings it reverts to previous settings
+ Also experiencing with Paypal, unable to change out of sandbox to live; will not hold change to API credentials.

All of this did work previously without issue. Everything else seems to be working fine.

Resolution attempts (without success):

+ Uninstall and re-install ProSites.
+ Deactivate all other plugins
+ Deactivate all themes

Any feedback to resolve would be greatly appreciated.