Hi Sam LEW,
Thanks so much for your advice here 
It actually got solved after I explored more in the forum and found this tool: Meta for Business (formerly Facebook for Business)
Turns out it was a connection issue – Make didn’t have lead access permission for the page. I used the testing tool to re-authorize it, and now everything is working perfectly 
Really appreciate you highlighting the support ticket route too – I’ll definitely keep that in mind for future issues.
Quick question though:
If I have multiple Facebook Lead Ads forms, is it possible to use multiple Facebook Lead Ads (New Lead) modules in the same scenario? Right now I’ve been duplicating entire scenarios for each lead form, which works but feels a bit clunky.
Would love your insight!