Good day, Joomshaper Team!
I, like many others it appears, have a unique issue with the forms happening, where the form just sits there after send is hit but an email is not actually sending and the redirect is not happening either.
I can confirm that the Joomla email sending capability (SendMail via php) is working fine within Joomla itself (Send Test email button works in Global Configuration). I can also confirm this happens on all SP Page Builder Forms, regardless of the form. Doesn't matter if its a new form, or an existing form that has worked before.
The captcha also resolves correctly, and that I have caching turned on but I don't know what else could be wrong. I also looked at the documentation you have.
This happens on my sandbox website and my live website. Please see the login credentials below and please let me know how you fixed it, so that I can apply the same to my live site.