Favouring the proposal to have an advertising campaign (9)
I believe the answer is:
promotion
'an advertising campaign' is the definition.
(I've seen this before)
'favouring the proposal' is the wordplay.
'favouring' becomes 'pro' (being in favour of something).
'the proposal' becomes 'motion' (proposal at a meeting).
'pro'+'motion'='PROMOTION'
'to have' acts as a link.
(Other definitions for promotion that I've seen before include "Puffing, perhaps" , "that should result in more money" , "Advancement" , "Advertising campaign" , "Step up" .)