Field on Document Header using BAPI for posting

Hi there.

I need to fill the BKPF-BRNCH field (the Branch Number header field in transaction FB01) to post a document by means of the BAPI_ACC_DOCUMENT_POST function module, but I haven't find the field in the DOCUMENTHEADER table, and I can't figure out how to fill it.

Can anyone help me...?

Thanks in advance.