The most common and most likely answer to this crossword clue is the 9 letter word REIMBURSE
I've seen this crossword clue in Financial Times
R
E
I
M
B
U
R
S
E
More clues leading to the result REIMBURSE
- Pay back bruiser, with me being beaten up
- Hanger-on in French city initially expecting pay back
- Doctor supporting German state missing church and sure to arrange refund
- Refund Earl following massage upset in bubbly French spa
- Pay back unfortunate slumberer I left out
- Repay bruiser upset with me
- Give back pound from mouldy mulberries
- Pay out for back rub in place known for champagne and ecstasy
- To indemnify French cathedral site, European must encase rough edge
- Return pounds spent in cultivation of mulberries
Buddy explains!

The straight part
We know that "Pay back" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pay back = reimburse.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 REIMBURSE mean?
REIMBURSE verb- To compensate with payment; especially, to repay money spent on one's behalf.