Credit people having failed exam (4)

I believe the answer is:

amex

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'credit people' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

'failed exam' is the wordplay.
'failed' is an anagram indicator.
'exam' is an anagram of 'AMEX'.

'having' acts as a link.

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I've seen this clue in The Guardian.

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