CURL -F file push -> convert to equivalent PowerShell Invoke-RestMethod - powershell

Question

I have seen a ton of attempts to do this in Stack Overflow, but none of the approaches have worked for me (and many others). But it seems like a simple thing to do:
This curl command works fine in powershell.
function curlPush() {
$url = "$post_url/$dset_id/transactions/$trid"
$header = "Authorization: Bearer $token"
curl.exe --request POST --url $url --header $header -F file="#$folder_path"
}
However the equivalent using Invoke-RestMethod gives an error:
function pushFile() {
$url = "$post_url/$dset_id/transactions/$trid"
$header = #{
'Authorization' = "Bearer $token"
'Content-Type' = 'multipart/form-data'
}
$response = Invoke-RestMethod -Uri $url -header $header -Method POST -InFile $folder_path
if (!$?) {
Write-Host $_.ErrorDetails.Message
}
$response
}
The error returned is:
Invoke-RestMethod : {"errorCode":"INVALID_ARGUMENT","errorName":"Default:InvalidArgument","errorInstanceId":"0bc80c74-35ae-4837-a87e-ff0e214b451b","parameters":{}}
At C:\Users\Documents\Software Projects\SolarWinds\PushFiles.ps1:42 char:17
+ ... $response = Invoke-RestMethod -Uri $url -header $header -Method POST ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (System.Net.HttpWebRequest:HttpWebRequest) [Invoke-RestMethod], WebException
+ FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeRestMethodCommand
Any suggestions?