# Wait for Callback

## Wait for an external system to initiate a callback

> The Wait for Callback node was created to facilitate an asynchronous process external to Chat Flow. For example waiting for an external client system to generate an invoice.\<br />\<br />This node will block the flow until a callback was received or the timed out was reached. The timeout is 1 minute less that the session length.\<br/> \<br />This node should be used in conjunction with the Set Variable Node to first set a UUID as a variable and then use that UUID in the Reference Field on the node and in the Callback API so that the Callback Handler can identify that the callback belong to a specific session.\<br />\<br/>Once the callback is received the end-user can then continue with the conversational workflow according to the steps defined in Flow.

```json
{"openapi":"3.0.1","info":{"title":"Flow","version":"1.1.0"},"servers":[{"url":"https://flow-callback.clickatell.com/","description":"Production server"},{"url":"https://control-callback-uat.payd.co/","description":"Sandbox/UAT server"}],"paths":{"/chat/callback":{"post":{"tags":["Wait for Callback"],"summary":"Wait for an external system to initiate a callback","description":"The Wait for Callback node was created to facilitate an asynchronous process external to Chat Flow. For example waiting for an external client system to generate an invoice.<br /><br />This node will block the flow until a callback was received or the timed out was reached. The timeout is 1 minute less that the session length.<br/> <br />This node should be used in conjunction with the Set Variable Node to first set a UUID as a variable and then use that UUID in the Reference Field on the node and in the Callback API so that the Callback Handler can identify that the callback belong to a specific session.<br /><br/>Once the callback is received the end-user can then continue with the conversational workflow according to the steps defined in Flow.","parameters":[{"name":"reference","in":"header","description":"A reference to be passed as a header.","required":true,"schema":{"type":"string"}}],"requestBody":{"description":"Payload describing the callback result","required":true,"content":{"application/json":{"schema":{"$ref":"#/components/schemas/Waitforcallback"}}}},"responses":{"202":{"description":"Successfully validated the response and returned data appended to matched session."},"204":{"description":"Callback has previously been processed in is being ignored."},"400":{"description":"A bad/invalid reference was returned and the session could not be matched, or the session has expired."}}}}},"components":{"schemas":{"Waitforcallback":{"type":"object"}}}}
```


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