The most common and most likely answer to this crossword clue is the 8 letter word CONTANGO
C
O
N
T
A
N
G
O
More clues leading to the result CONTANGO
Buddy explains!

The straight part
We know that "payment for postponement of delivery" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case payment for postponement of delivery = contango.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 CONTANGO mean?
CONTANGO noun- The situation in a futures market where prices for future delivery are higher than prices for immediate (or nearer) delivery.
- The amount by which prices for future delivery are higher than prices for near delivery.
- (London Stock Exchange) Fee paid by a buyer to the seller on settlement day when the buyer wishes to defer settlement until the next settlement day.
- (London Stock Exchange) To charge (a buyer) a fee to defer settlement until the next settlement day.