How to debug FB01

Hi Experts,

I am trying to post an FI document manually through FB01 and when I put a break point at FM BAPI_ACC_DOCUMENT_POST, it didn't stop. I am thinking that FB01 might be using BDC or LSMW when "SAVE". Do not know how to figure out which one it is using. Appreciate if anybody could guide me how to fins what FB01 is using at background to post a document when "SAVE".

Thanks,

Nani