500 internal Server Error when trying to update an attachment using Powershell

[Julien Henning]

I want to update an json file in confluence using the Api and Powershell 

---

$pageId = "2226721108"  # Replace with the actual page ID

$attachmentId = "2238705975"  # Replace with the actual attachment ID

$apiUrl = "https://HereIsOurServer/confluence/rest/api/content/$pageId/child/attachment/$attachmentId/data"

$proxy = "ourProxy :)"

$headers = @{

    "Authorization" = "Bearer $authToken"

    "X-Atlassian-Token" = "nocheck"

    "Content-Type"="multipart/form-data"

}

$body =@{

    "file" ="StatusTestclients\JiraUpdateTestClients\result.json"

    "minorEdit"=$true

    "comment"="new"

}

# Send the POST request to update the attachment file

Invoke-RestMethod -Uri $apiUrl -Headers $headers -Method Post -Body $body -Proxy $proxy

And here the error i get 

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Invoke-RestMethod : Der Remoteserver hat einen Fehler zurückgegeben: (500) Interner Serverfehler.
In C:\Users\WAETEI1\Desktop\toolsetprelive\StatusTestclients\JiraUpdateTestClients\UpLoadDataToConfluence.ps1:19 Zeichen:1
+ Invoke-RestMethod -Uri $apiUrl -Headers $headers -Method Post -Body $ ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (System.Net.HttpWebRequest:HttpWebRequest) [Invoke-RestMethod], WebException
+ FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeRestMethodCommand

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Now is the question what im doing wrong