PJIANG: help- How to use AP I-94 for SSN Application?

PJIANG: 拿 AP 的 I-94 去申請 my son's SSN卻被打了回來, SSA office said: They could not find either code or class on I-94 (in I-94, Purpose: AOS). What is class or code for SSN application using AP I-94? Do I have to apply EAD for my son first? My son just are 8-year old.

Thanks