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Introduction
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Introduction

Welcome to the InstaMessage API.

The InstaMessage API allows you to send and receive messages across SMS, WhatsApp, Messenger, and RCS using a single, unified interface.

This page provides a high-level overview of how the API works, where to send requests, and how authentication is handled.

Base URL

All API requests are made to the following base URL:

https://api.instamessage.co.uk/v1

All endpoints described in this documentation are relative to this base URL.

Authentication

All requests must be authenticated using an API key.

Authentication is performed by including your API key in the Authorization header:

Authorization: Bearer YOUR_API_KEY
Content-Type: application/json

For details on obtaining and rotating your API key, see Authentication → API Keys

Core concepts

Unified messaging endpoint

Most outbound messaging is handled through a single endpoint:

POST /messages

This endpoint is used to send:

  • SMS messages
  • WhatsApp messages (Template and free-form)
  • Messenger messages
  • RCS messages (text, media and rich cards)

The behaviour of the request is controlled by fields such as:

  • channel
  • message_type
  • Message content (text, template, image, video, audio, file, custom, etc...)

Asynchronous delivery

Sending a message is an asynchronous operation.

This means:

  • A successful API response confirms the request was accepted for processing
  • It does not guarantee that the message was delivered
  • Final delivery status is reported later via:
    • Webhooks
    • Message status endpoints

Contacts are created automatically

When you send a message to a phone number for the first time:

  • A contact is automatically created
  • The phone number becomes the unique identifier
  • Additional details can be added later using the Contacts API

You do not need to create contacts before sending messages.

Contacts are created automatically the first time you send a message to a new phone number.

However, if you want to store additional details (such as names, email addresses, or custom_fields), we recommend creating or updating contacts explicitly using the Contacts API.

Supported channels

InstaMessage supports the following channels:

  • SMS
  • WhatsApp
  • Messenger
  • RCS

Each channel has its own rules around initiation, Templates, media, and read receipts. These differences are explained in the Messaging Overview and channel-specific guides.

Environments

InstaMessage currently provides a single production environment.

All API keys and requests operate against the live platform.

Sandbox and test environments will be added in future versions.

API versioning

The current API version is:

v1

Breaking changes will result in a new versioned base path.

Next steps

Once you understand the basics, you can explore:

This overview is the starting point for all InstaMessage API integrations.

Authentication