Hi @bbarrett!
The reason you are seeing this is that the PO has Multiple Vendors as a vendor, which means that not all of those products are from the same vendor.
The ID you are seeing in return is "vendor_id": "VmVuZG9yOjA=", which is Base64 encoding of Vendor:0
When there is no Vendor assigned to the PO we default that value to Multiple Vendors
Let us know if that doesn’t help, if we could explain better or if there is anything else we could help with.
Thanks in advance!
Tom