# Wait For Callback

The *Wait for Callback* node is used to facilitate an asynchronous process external to Chat Flow and continue the flow when a callback is received.

This node will block the flow until a callback is received or the session times out.

{% hint style="info" %}
To use this node, the [Wait For Callback API](https://docs.clickatell.com/products/flow/external-link-handler-api-reference/#tag/Wait-for-Callback) needs to be set up.
{% endhint %}

{% hint style="warning" %}
This node must be used in conjunction with the [*Set Variables*](https://guides.clickatell.com/flow/action-nodes/action-nodes-set-variables) node. The *Reference* that is being set is the variable from the *Set Variable* node.
{% endhint %}

<figure><img src="https://content.gitbook.com/content/joAgInTNsBfDdfx1I23z/blobs/LznSHtvVQxltvnwh1siG/image.png" alt=""><figcaption><p>Setup of a Wait For Callback node</p></figcaption></figure>

<figure><img src="https://content.gitbook.com/content/joAgInTNsBfDdfx1I23z/blobs/8oPLI209aSNywNq5BRVh/image.png" alt=""><figcaption><p>Example flow containing Wait For Callback node</p></figcaption></figure>