[Hustle Pro] Hustle will not connect to Mautic

I have a site where Hustle will not connect to it’s Mautic installation. It will connect to other Mautic installations but not the one specifically built for it. I installed Mautic as a sub-directory this time. I normally install it on another server with a sub-domain. I first thought the sub-directory installation might be the problem until I built another Mautic installation on another server using a sub-domain of the site and it also would not connect. API and HTTP Basic Auth are enabled. I have deleted Hustle and reinstalled it. Permissions are all the same as other working sites. I have recreated the site and its Mautic install on its own DigitalOcean Droplet and still it will not connect. I’m totally stumped. Do you have any suggestions?