A vendor must be authorized before submitting a BPA for posting onto GSA Advantage! The list of authorized vendors and BPAs are located here
SIP Vendors - The SIP program helps vendors produce a separate BPA catalog and submit to GSA for posting onto GSA Advantage!
EDI Vendors - A separate catalog file must be sent for a BPA posting. An additional REF segment (1/050) in the header must be included in the X12 file using the “BB” qualifier in the REF01 and the actual BPA number in the REF02.
For example: REF*BB*N00104-xx-x-xxxx