unable to successfully get FulfillmentInboundService getLabels call to work

[solverware]

I am trying to verify I'm using the GetLabels method from the FulFillmentInboundService to work. I am using the test case that Amazon provides for their sandbox. I get the error message:

"Parameter shipmentId has been specified as both a path parameter and a query parameter." Please advise!

public string GetLabelUrl(string shipmentID, AmazonCredential amazonCredential)
{
var service = new FulFillmentInboundService(amazonCredential);
var label = new ParameterGetLabels();
label.PageType = FikaAmazonAPI.Utils.Constants.PageType.PackageLabel_Letter_2;
label.LabelType = FikaAmazonAPI.Utils.Constants.LabelType.BARCODE_2D;
label.shipmentId = "348975493";
LabelDownloadURL url = null;
try
{
url = service.GetLabels(label);
}
catch (Exception exc)
{
throw;
}

return url.DownloadURL;

}