New-ZabbixHostGroup - failed when name include danish characters (UTF8)

[christensenjohn]

$a = Invoke-RestMethod "$URL/api_jsonrpc.php" -ContentType "application/json" -Body $BodyJSON -Method Post
if I add charset=utf8 it works.
$a = Invoke-RestMethod "$URL/api_jsonrpc.php" -ContentType "application/json; charset=utf-8" -Body $BodyJSON -Method Post