I was playing with my mautic landing pages on my laptop and I noticed the form was hanging at “please wait” instead of redirecting. It appears that the redirect URL must be hosted the same as the form. Since shopify requires all sites be served using https, and my server was not requiring this, I had logged into mautic over insecure http on my laptop. It took my a while to figure out that was what was making the form hang. The simplest solution to this is to modify your virtual hosts file to redirect http requests to the https site.
You can follow these instructions: https://www.namecheap.com/support/knowledgebase/article.aspx/9821/38/redirect-to-https-on-apache
In the line that is
Redirect permanent / https://www.yourdomain.com/
do not forget the ending “/” or else the redirect will fail
I typoed that the first time and redirects were failing, what’s worse my browser caching was preventing changes from seeming to take effect. It’s a good idea to test your pages in a new anonymous/incognito whatever your browser calls it window so you know caches and cookies and such aren’t affecting anything.