Button of final step is loading forever

When hitting the button for the final step, it might be that this takes forever. First of all, make sure there are no JavaScript errors in the Error Console - they could be preventing further JavaScript execution.

Another possible cause is that mails simply take a long time to send. For example, if your server uses a default MTA (like Sendmail or Postfix) it might be that SMTP communication with external servers is delayed or even denied. To check for this, temporarily disable all mail communication (set system/smtp/disable to 1) to see if this helps.