Groovadelickun

My wife applied for AOS (from a K1 visa) and during our AOS Interview she got grilled on her CCP membership.
She also was only a member as her high level of education and pressured to join but didn't pay the fees and was finally able to get a resignation letter from her local CCP office.
 
We still thought the interview went well overall but they said they would let us know as "they did not have all the paperwork to make a decision" (I thought that was odd)
We later received a denial due to her prior membership in the CCP so we filed a i-601 and now the long wait....
 

Yes, I don't think you can schedule the appointment until P4 has been received. I'm attaching an except from the P4 email we received. The second bullet point is the one talking able scheduling the appointment.