Moorland apartment was not successful (4,4)

I believe the answer is:

fell flat

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'not successful' is the definition.
I can't tell whether this defines the answer.

'moorland apartment' is the wordplay.
'moorland' becomes 'fell' (fell can mean a moor).
'apartment' becomes 'flat' (synonyms).
'fell'+'flat'='FELL FLAT'

'was' is the link.

Can you help me to learn more?

(Other definitions for fell flat that I've seen before include "failed to impress" , "collapsed" , "provoked no interest" .)

I've seen this clue in The Daily Express.

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