Inadvertently includes promo (6)
I believe the answer is:
advert
'promo' is the definition.
(I know that advert is a type of promo)
'inadvertently includes' is the wordplay.
'includes' says the answer is hidden in the clue.
'ADVERT' is hidden in the letters of 'inadvertently'.
(Other definitions for advert that I've seen before include "Refer to the red vat" , "Call attention or allude to" , "Public notice" , "piece of publicity" , "Refer; commercial" .)