Performing a HTTP Form Post To Third Party Vendor Using PeopleSoft IB Services?

I have a requirement to invoke a 3 rd party web services API via Peoplesoft IB.

We are on Peopletools 8.58

I am using IB REST operation and the method is POST. The API request consists of file uploads(PDF/PNG/JPEG) and the type of request in the body is form-data. Basically, the API consumes multipart/form-data and produces application/json. But Peoplesoft IB does not support multipart/form-data as content type.

So, I am trying to set the content type in the PeopleCode as follows

&msg.IBInfo.IBConnectorInfo.AddConnectorProperties("Content-Type", "multipart/form-data boundary=TheBoundary", %Header);

But IB response is coming back as error HTTP code- 400 Bad Request