add_months function causing, invalid relational operator error

I want this query to pull 24 month past data,

so I appended add_months(p.month,-24)

However, this query results in an error:invalid relational operator due to add_months condition

abc@def>select r.pfizer_account_id,
  2   p.presc_num,
  3   spm.product_id,
  4   p.month,
  5   t.best_call_state,
  6   sum(p.trx_count)
  7  from ops$pyrcm.rlup_assigned_account r,
  8   adhoc.temp_presc_num_TEST t,
  9   retail.prescrip_retail partition (PRESC200705) p,
 10   sherlock.sherlock_product_mapping spm
 11  where spm.product_id like '056%'
 12   and add_months(p.month,-24)
 13   and spm.mds6 = p.product_id
 14   and t.CLIENT_ID = p.presc_num
 15   and r.pfizer_account_id = p.payer_plan
 16   and t.best_call_state = r.ST
 17  group by r.pfizer_account_id,  
 18   p.presc_num,
 19   spm.product_id,
 20   p.month,
 21   t.best_call_state;
 and spm.mds6 = p.product_id
 *
ERROR at line 13:
ORA-00920: invalid relational operator