How to setup HTTPRequest of type multipart/mixed with boundary properly in Wolfram Language?

I am trying to query the Tableau REST API using Wolfram. I have been able to send all the other types of HTTPRequest to it without issues but for some reason whenever the Body is multipart with mixed types separated by boundary I can't get it to work.

My request is as follows:

HTTPRequest[
    $server<>"/api/3.22/sites/"<>$site<>"/workbooks?workbookType=twb&overwrite=true",
    <|
        "Method"->"POST",
        "Headers"-><|"X-Tableau-Auth"->$token,"Content-Type"->"multipart/mixed; boundary="<>$boundary,"Accept"->"application/json"|>,
        "Body"->StringRiffle[{
            "--"<>$boundary,
            "Content-Disposition: name=\"request_payload\"",
            "Content-Type: text/xml",
            ExportString[XMLElement["tsRequest",{},{
                XMLElement["workbook",{
                    "name"->$workbook,
                    "showTabs"->"false",
                    "description"->"This is a test workbook!"
                },{
                    XMLElement["views",{},{
                        XMLElement["view",{"name"->$view,"hidden"->"true"},{}]
                    }],
                    XMLElement["project",{"id"->$project},{}]
                }]
            }],"XML"],
            "--"<>$boundary,
            "Content-Disposition: name=\"tableau_workbook\"; filename=\""<>FileNameTake@$file<>"\"",
            "Content-Type: application/octet-stream",
            Import[$file,"Text"],
            "--"<>$boundary<>"--"
        },
            "\n"
        ],
        "Expect"->"100-continue",
        "Content-Length"->ToString@StringLength@Import[$file,"Text"]
    |>
]

I keep getting the error:

{"error":{"summary":"Bad Request","detail":"Payload is either \
malformed or incomplete (Could not parse multipart servlet request; \
nested exception is \
org.apache.commons.fileupload.FileUploadException: Header section has \
more than 10240 bytes (maybe it is not properly \
terminated))","code":"400000"}}

Please help this is a critical piece that is breaking my workflow. Please suggest any changes and I can make as many attempts to get it to work.

I am not sure how to send the content of the file, I assume this Import[$file,"Text"] is not right or Wolfram is messing up the multipart request somehow.