The most common and most likely answer to this crossword clue is the 9 letter word PACKAGING
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More clues leading to the result PACKAGING
Buddy explains!

The straight part
We know that "Promo" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case promo = packaging.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PACKAGING mean?
PACKAGING verb- To pack or bundle something.
- To travel on a package holiday.
- To prepare (a book, a television series, etc.), including all stages from research to production, in order to sell the result to a publisher or broadcaster.
- The act of packing something.
- The materials used to pack something.
- The industry that produces such material.
- (by extension) The manner in which a person or product is promoted.