> ## Documentation Index
> Fetch the complete documentation index at: https://www.cometchat.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Properties and Constraints

> Properties and Constraints for CometChat REST API.

Properties and constraints for the Notification APIs.

## Push Notifications

| **Property**                   | **Constraints**            |
| ------------------------------ | -------------------------- |
| Maximum FCM providers per app  | Contact support for limits |
| Maximum APNS providers per app | Contact support for limits |
| Maximum push tokens per user   | 100 active tokens          |
| Push token value               | Max 4,096 characters       |

## Email Notifications

| **Property**                | **Constraints**                |
| --------------------------- | ------------------------------ |
| SendGrid API key            | Required for SendGrid provider |
| Custom provider webhook URL | Must be a valid HTTPS URL      |

## SMS Notifications

| **Property**                | **Constraints**              |
| --------------------------- | ---------------------------- |
| Twilio Account SID          | Required for Twilio provider |
| Twilio Auth Token           | Required for Twilio provider |
| Custom provider webhook URL | Must be a valid HTTPS URL    |