​Uploading Attachments via Rest API in IFS Cloud

Hello, I am trying to upload an attachment (to a customer order in this example) in IFS Cloud via the Rest API. I am following the documentation found in this post: https://community.ifs.com/technology%2Dinfrastructure%2Dcloud%2Dintegration%2Ddev%2Dtools%2D50/upload%2Ddocument%2Dvia%2Dcreateandimportdocument%2Dsvc%2Dedmfileset%2D6284?postid=23329#post23329

I understand the process has 4 parts:

1. Create the document
2. Attach the document to an object (Customer Order in this case)
3. Ask for an upload URL for the attachment
4. Upload the attachment. 

I have successfully performed items 1-3 via postman, and received my upload URL: 

https://[MY IFS SERVER]/int/ifsapplications/projection/v1/CreateAndImportDocument.svc/EdmFileSet(DocClass='AGREEMENT',DocNo='1551348',DocSheet='1',DocRev='A1',DocType='ORIGINAL',FileNo=1)/FileData

When i try to upload my document, i receive this response:

{
    "error": {
        "code": "ODATA_PROVIDER_ERROR",
        "message": "An internal server error occurred. Contact administrator.",
        "details": [
            {
                "code": "PROJECTION_IMPL_EXCEPTION",
                "message": "Error when writing the file: Error while uploading the file. Detail: null"
            }
        ]
    }
}

I have tried in both postman and python via requests module and i receive the same error. This is what my postman request looks like: 
 

Any idea what i am doing wrong here?