Student or Learner
A: Must I pay now?
B: No, you needn't. / No, you musn't.
A: Need I pay now?
B: Yes, you must. / Yes, you need.
They are my sentences. I would like to ask whether or not all the answers are possible, depending on the context.
Would you mind telling us what answers are natural?
No, you don't have to [pay now].
Yes, you have to pay now.
Yes, you must pay now.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.