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A callback is a URL OneXtel calls when something happens to a message — it was delivered, it failed, the recipient replied, or they tapped a link. Register the URL once against an API key, and every message sent with that key reports back to your system. Callbacks are configured per API key and per channel, so the same account can send delivery reports for WhatsApp and RCS to different endpoints, or route two products’ traffic to two different systems.
An API key with no callback registered still sends messages perfectly well — it reports nothing back. If messages are arriving but your system never hears about them, an unregistered callback is the first thing to check.

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Add a callback

1

Open the Config section

In the left pane, click Config, then select the Callback Configuration tab.
2

Start a new callback

Click + Add New Callback to open the Create Callback dialog.
3

Set the basic configuration

4

Set the request configuration

5

Set the throughput limit

Enter a TPS value to cap how many callback requests per second OneXtel sends you. Set it to what your endpoint can absorb; a limit that is too high will cause dropped callbacks if your endpoint cannot keep up.
6

Add headers, if required

Enter a header Key and Value, then click + to add it. Use Delete to remove a header, or Reset to clear the form.Some integrations require a specific header — see Headers.
7

Create

Click Create. The callback appears in the Callback Configuration list with its title, channel, method, URL, parameters, headers, TPS, and status.
Callback Configuration tab listing a callback with channel, method, URL, parameters, TPS and status

Callback Configuration list

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Choosing default parameters

Only the parameters you select are sent. Pick the ones your system actually needs — a smaller payload is faster to process and easier to parse — but include enough to correlate the callback with the original message. At minimum, select the message identifier so callbacks can be matched to sends. The custref1–custref5 custom reference fields are echoed back exactly as you set them on the original send, which makes them the simplest way to carry your own campaign or order IDs through to the callback. For the parameters available per channel, see:

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Headers

Headers are how a callback carries authentication or routing information the receiving system requires. Two common cases:
  • Authentication. If your endpoint expects a token or API key, add it as a header rather than putting it in the URL.
  • Onward routing. Some connectors need the destination URL passed so they can forward the callback to a third-party platform. The MoEngage plugin, for example, takes it in a header named callback on RCS and SMS. Its WhatsApp inbound callback is the exception: there the URL goes on the Callback URL itself as a callback_url query parameter, not a header.
Never put credentials in the Callback URL itself. URLs are logged along the request path; headers are the correct place for anything sensitive.

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One callback per event type

A callback covers a single event type, so an integration that needs delivery reports and inbound messages and button clicks needs a separate configuration for each — same channel, same API key, different type and URL. This is why plugin setup often involves creating two or three callbacks in a row. See the MoEngage or WebEngage setup steps for a worked example.