Google Tag Manager Tracking For Facebook Ads

I need some help with Google Tag Manager triggers to get set up for Facebook ad campaigns.

We have our Facebook Pixel set up using Facebook Template for GTM by  Facebookarchive. All the tags we have set up so far with this are firing fine.

However, I'm having trouble setting up a tag and trigger to track registrations for courses on our site (we use WordPress and LearnDash).

When a user registers (in this case for an online course), the registration form loads in a modal.

When the user completes the form to register for a course, the main window displays a url that ends with ?ld-registered=true#login

I've tried several triggers, including "Page View Window Loaded" and "Page View" with the condition set to only trigger when Page URL ends with ?ld-registered=true#login.

But I just can't get the tag to trigger when the modal form is completed.

I suspect this would take a GTM expert an hour or two to create the right tag and trigger, so while this isn't a major job, we'll need further help with other GTM tags and GA set ups