Unable to find parameter Orderer

Can anybody tell me what would be the value of parameter “orderer” in Post API of ORDER.because i m each time getting error “orderer cannot be null” while using post API.

Please clear my questions:

1.In which table i can use this column “orderer”.Please tell me table which contain this table.

2.Is it is a table if yes then please give me schema of this table.

Can you share the full data that you are posting, the url you are posting to, and the full stack trace of the error?