It's awful waiting for the black mass (3,7)

I think it could be either:

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3,7

10*

bad service

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'the black mass' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'it's awful waiting' is the wordplay.
I cannot really see how this works, but
'awful' could be 'bad' (similar in meaning) and 'bad' is found within the answer.
'waiting' could be 'service' (I've seen this before) and 'service' is located in the answer.
No letters remain.
This may be the basis of clue (or it may be nonsense).

'for' acts as a link.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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