The most common and most likely answer to this crossword clue is the 12 letter word PRECONDITION
I've seen this crossword clue in Independent
P
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C
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N
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Buddy explains!

The straight part
We know that "Up-front requirement" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case up-front requirement = precondition.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 PRECONDITION mean?
PRECONDITION noun- A requirement which must be satisfied before taking a course of action.
- To condition in advance