I was able to get a redirect to the page I wanted to show after registering (https://play2progress.com/pages/memberships) using the temp create account page I set up at https://play2progress.com/pages/sign-up. However, it wouldn't show the form again w/ an error for signing up using an already-used email (would just always redirect to the memberships page).
After trying a few things out, I realized that possibly one of the main issues was using a different page from the default (https://play2progress.com/account/register) to test my registration. I'm using https://play2progress.com/pages/sign-up instead to test a flow where successful submission of the form redirects the user to the memberships page. However, the problem was that if the email address entered is already in use, the user wouldn't know and would simply be moved to the captcha stage and then to the memberships page but not as a logged in, newly created user.
I thought perhaps the issue was the captcha (b/c it gave us no way to know whether the form submission would be successful) and thus asked for it to be disabled. Unfortunately, that ended up w/ the same result as w/ the captcha. If I removed my additions (i.e. code in theme.liquid that added a hidden input on the captcha form to redirect_to the memberships page), I was able to see the error on the 'official' sign up/register page at https://play2progress.com/account/register.
Do you know how I'd be able to 1) see the error for entering an already in-use email address 2) redirect the user to the memberships page after successful account creation AND 3) test w/ my temporary sign-up page [/pages/sign-up]? If having all 3 happen isn't possible, is having 1 & 2 both happen possible if we make the styling & redirecting changes we want to the page at /account/register? Also, would adding the captcha back in still allow both 1 & 2 to work?