In the Dialogflow CX console, choose the project and the agent.

In the CX agent screen, go to the Build tab. Choose the required flow and the required page (Start/End Flow/End Session) in this flow in which a fulfillment is needed from the contact center application.

Under the Routes section, define a route and conditions that satisfy the custom exit criteria for triggering the transition.

In this route, under Fulfillment section, click Add dialogue option and choose Custom payload.

Add the custom payload of type Execute_Request that defines the payload to be sent from CX in the following format:

{
"Execute_Request":{
"Event_Name": "<Name of the event>", 
"Data" : { 
"Params":{ 
"<param1 name>": "<param1 value>", 
"<param2 name>": "<param2 value>"
}

Choose Page in the Transition section to set the transition to the same page when the flow resumes.

Create an event handler and provide the event name in the flow builder application. For more information, see https://cloud.google.com/dialogflow/cx/docs/reference/rest/v3/EventHandler.