Someone's not buying it.

[Aaron]

Rachel: Hi! Well, we were just about to take off and see a movie. Oh no!
Erin: What’s wrong?
Rachel: Oh Phoebe, we forgot that party we have to go to.
Phoebe: Oh no.
Joey: (skeptical) What party?
Phoebe and Rachel: A birthday party.
Joey: Who’s birthday party?
Phoebe and Rachel: Alison’s birthday party.
Joey: (still skeptical) Oh, and how old is Alison?
Phoebe and Rachel: 32. (Joey’s not buying it.)
Rachel: (does a retching sound) Wait a minute! Why don’t you guys do something?!
Joey: (still skeptical) Yeah, look how that worked out.

=>
Ok, "Joey's not buying it" means Joey still doesn't believe them saying?

[Casiopea]

Joey doesn't believe them.