Problem Solved!
I’m going to leave this here as I don’t believe I’ve seen any information regarding this type of error and I think it will be helpful to others, in fact, I think this needs to be highlighted in Brave documentation somewhere.
Turns out that if you meet all the criteria to receive ads but none are coming through, then it could be an extension that is causing the issue.
For me, ads were not coming through because of a Picture-in-Picture extension. Once I removed the offending extension, I re-checked the catalogue link again and it was fully populated!!
Hope this helps anyone else experiencing issues.