The most common and most likely answer to this crossword clue is the 11 letter word ERROR-PRONE
E
R
R
O
R
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P
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E
Buddy explains!

The straight part
We know that "Inept" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case inept = error-prone.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 ERROR-PRONE mean?
ERROR-PRONE adjective- In the habit of making errors.