Mule ESB allows creating dynamic payloads like JSON, XML, or text. This document demonstrates how to dynamically generate a JSON payload in a Mule flow and send it to an external service. The JSON is constructed using Mule expression transformers, which execute expressions to set the payload. Flow variables are used to populate the JSON elements, but values could also come from inbound properties or other dynamic sources. Testing the flow by hitting a URL generates the JSON request and posts it to the external service, returning a response.