Acknowledgment of payment (7)
I believe the answer is:
receipt
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">acknowledgment of payment</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for receipt that I've seen before include "Proof of purchase" , "old cook's directions" , "A written acknowledgement; a word used in the first ever 2 dn" , "Perhaps slip" , "Evidence of sale" .)