PSA: How to bind PSN account to Infold Games
Good god I figured it out!
On the desktop browser (best to do this on the computer or desktop mode on mobile), go to https://account.infoldgames.com/login and sign in by clicking on the PlayStation icon (and check the box for Terms of Service). After signing in, go to the Account Info tab and bind an email address and create a password. Now you're bound and you should be able to sign into your Infold account when you access the web event!
