Invoke-WebRequest in an own function with arguments - powershell

Question

I am trying to run an Invoke-WebRequest command on PowerShell Core 6.3 on a Ubuntu system with the following settings to create a forwarder:
$userLocalMailPart = "user"
$userGlobalMailPart = "Hotmail.com"
$address = "Some Address"
$pair = $login + ":" + $password
$bytes = [System.Text.Encoding]::ASCII.GetBytes($pair)
$base64 = [System.Convert]::ToBase64String($bytes)
$basicAuthValue = "Basic $base64"
$url = "https://" + $server + ":" + $port + "/Domain/ObjectList.html"
$headers = #{"Authorization" = $basicAuthValue;
"Referer" = $url
}
$body = #{
"NewForwarderName" = $userLocalMailPart ;
"NewForwarderAddress" = $address;
"CreateForwarder" = "Create Forwarder"
}
$result = Invoke-WebRequest `
-Uri $url `
-SkipCertificateCheck `
-Method 'POST' `
-Headers $headers `
-Body $body
This runs perfectly. No error and the forwarder is successfully created.
Now I want to use a function like this:
[Web]::requestHeaderContent($url, $headers, (ConvertTo-Json($body)), 'POST')
[object] static requestHeaderContent([String] $url, [hashtable] $headers, [Object] $body, [String] $meth) {
Invoke-WebRequest `
-Uri $url `
-SkipCertificateCheck `
-Method $meth `
-Headers $headers `
-Body $body
}
The variables like headers and body are the same. I also tried it with ConvertTo-Json but it just don’t work. I also receive a Success 200 Code but the forwarder is not created. I guess my problem are the parameters. Any idea what I am doing wrong?
Thanks
Stephan