Are you going to pay up? I won't ask you again! (4,6)

'are you going to pay up?' is the definition.
I know nothing about this answer so I can't judge whether this works.

'i won't ask you again' is the wordplay.
I cannot really understand how this works, but
'i' could be 'a' and 'a' is found within the answer.
'ask' could be 'demand' (synonyms) and 'demand' is present in the answer.
The remaining letters 'lst' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?