Is it possible to create custom app like Twilio using own api endpoints?

Hi @dev13,

Absolutely, you can create custom apps using the Zendesk Apps Framework although you can't send an SMS via the API. You can create triggers that will fire SMS notifications though, so this might be helpful depending on your use-case. Here's a couple of guides that will help you get started:

Zendesk Apps Framework: Getting Started
Building Your First Support App
Using Text Notifications with Triggers

Once you're ready to publish your app to the Zendesk marketplace, you can follow the guide here:

Submit you app

I hope this helps!

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