Make sense of publicity trick, mostly (3,2)
I believe the answer is:
add up
'make sense' is the definition.
(synonyms)
'publicity trick mostly' is the wordplay.
I cannot really see how this works, but
'publicity' could be 'ad' (short for advert) and 'ad' is found within the answer.
The remaining letters 'dup' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'of' is the link.
Can you help me to learn more?
(Other definitions for add up that I've seen before include "Do sums" , "Point to a reasonable conclusion" , "Total; make sense" , "Aggregate, get total" , "Seem consistent or reasonable - arithmetically?" .)