Hi Howard, most often your webhook is expecting to receive JSON data. The default behavior is to parse that JSON data and make it available to future modules. In the "advanced settings" of the webhook, you could change this to JSON-passthrough -- which will not parse the data.
In 95% of use case that default setting works out fine. But if you want to strictly enforce some data structure, you can also use the Show Advanced Settings to create a data structure for validation (and subsequent mapping).
More details can be found here.