Call Custom Service with JSON Body in D365FO

        
FileUploadTemporaryStorageResult fileUpload = File::GetFileFromUser() as FileUploadTemporaryStorageResult;
System.IO.Stream stream = fileUpload.openResult();
str responceJson;

using (var reader = new System.IO.StreamReader(stream))
{
    responceJson = reader.ReadToEnd();

    TESTPOReceiptRequestContract contract = FormJsonSerializer::deserializeObject(
        classnum(TESTPOReceiptRequestContract), responceJson);

    new TESTPOReceiptService().processRecord(contract);
}