I got it to work. The problem was a couple of the product images, which had to be removed from the category. Does anyone know what the problem is exactly? Is it their height?
If I remove the url https://mywebsite.com/email-signup-thankyou and add text to the Text to replace the form with after a successful sign-up text box, I get the following message: {“success”:true}.
I got the redirect to work. It wasn’t the CHECKBOX SETTINGS-Redirect to this url after signing up (leave empty or enter 0 (zero) for no redirect) but rather the MAILING LIST SETTINGS URL that was controlling the redirect for my site.