Alert21 Guide

Step-by-Step Messaging and DLT Guides

Use these guides to understand the concepts behind production messaging before you integrate an API.

Published 5 September 2026 · Last updated 5 September 2026

View SMS API Open Quickstart

Priority Guides

What is DLT?
How DLT registration works.
What is a DLT Template ID?
What is a Sender ID/Header?
What is a Principal Entity ID?
SMS API integration guide.
Transactional vs promotional communication.
SMS delivery receipts explained.
SMS character/segment limits.
OTP SMS best practices.

Direct Answers

Frequently Asked Questions

Quick answers to common questions about Alert21 SMS API, telecom compliance, and developer integration.

What should I learn before integrating an SMS API in India?

Start with DLT registration, Principal Entity IDs, sender headers, content templates, SMS encoding and delivery receipts. Understanding these concepts helps your team prepare compliant message templates, estimate message segments and process delivery outcomes correctly before production integration.

Where should developers begin with Alert21?

Read the DLT guide if you are new to Indian commercial messaging, then follow the SMS API integration guide and developer quickstart. Use the delivery-receipt and character-limit guides when implementing status handling, retries, Unicode messages and billing calculations.

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