Tracking Newsletter Subscriptions in Meta Ads Manager: Need Help!

Hey, does anyone know how to track newsletter Subscriptions in Meta Ads Manager? I set up tracking using GTM based on this video, but it doesn't work

1.
In the FB Pixel, I see PageViews but not subscriptions
2.
Google Tag Assistant doesn't see any tags on my pages (https://vibe9.beehiiv.com and https://vibe9.beehiiv.com/subscribe) - but when I go to GTM, I see that tracking quality is excellent

Who can help?