REST API Invoking a Business Service to Insert an Attachment

Hi Team,

Im trying to insert attachment in IP version 22.2

can you please help me

i have gone through this PDF but no luck getting below error.

{

  "body": {

       "SiebelMessageIn": {

      "IntObjectName": "TestPRequestAttachmentIO",

      "ListOfTestprequestattachmentio": {

        "TestClient Portal Request Attachment BC": {

          "TeststParent Id": "1-7TKKRD",

          "TestCPReqFileExt": "txt",

          "PReqFileName": "ServiceREVUT2_DemoHuge_UN11",

          "TestCPReq Attachment Id": "5XAHcAMABLAEkAQwBCADcARABRAG8AZwBJAEMAQQBnAEkAbABSAHAAZ"

        }

      }

    }

  }

}

{

    "ERROR": "Required in argument 'SiebelMessageIn' not supplied for 'Insert' method in Business Service 'ACECPRequestAttachmentInsert'(SBL-DAT-00125)"

}

Referring below link

https://docs.oracle.com/cd/F26413_28/books/RestAPI/c-Invoking-BS-Insert-Attach-JSON.html#tj1028010