RingCentral Send Fax - Multipart Test (Bad Request)

# Pack the JSON DATA

$todestination = [pscustomobject]@()
$todestination += @{
    phoneNumber = "+14435551212"
    name = "Test Recipient"
}

### CONVERT FILE CONTENT TO BASE64 STRING
$FilePath = "$($env:TEMP)\TestFax.PDF"
$objFile = Get-ItemProperty -Path $FilePath
$FileData = [Convert]::ToBase64String([IO.File]::ReadAllBytes($FilePath))

# Create Attachment Param
$attachmentdata = "data:application/pdf;name=$((Get-ItemProperty -Path $FilePath).Name);base64,$($FileData)"

$RingCentralSendFaxJson = [pscustomobject]@{}
Add-Member -InputObject $RingCentralSendFaxJson -MemberType NoteProperty -Name attachment -Value $attachmentdata
Add-Member -InputObject $RingCentralSendFaxJson -MemberType NoteProperty -Name to -Value $todestination
Add-Member -InputObject $RingCentralSendFaxJson -MemberType NoteProperty -Name faxResolution -Value "High"
Add-Member -InputObject $RingCentralSendFaxJson -MemberType NoteProperty -Name coverPageText -Value "Have cover page text"

$RingCentralSendFaxJson = $RingCentralSendFaxJson | ConvertTo-Json

$accountId = "~"
$extensionId = "~"

#Send the text message
$sendresponse = Invoke-RestMethod -Uri "https://platform.devtest.ringcentral.com/restapi/v1.0/account/$($accountId)/extension/$($extensionId)/fax" -Method Post -ContentType "multipart/form-data" -Body $RingCentralSendFaxJson -Headers $accesstoken.Header