# "How to Connect an External SMS API to On-Chat"

> "On-Chat's External API channel lets you connect any custom SMS provider or messaging gateway to your shared inbox by configuring a webhook endpoint and API credentials."

URL: https://on-chat.live/guides/how-to-connect-an-external-sms-api-to-on-chat/
Last updated: 2026-11-14

## Introduction
On-Chat's External API channel integration allows you to connect any custom SMS provider, in-house messaging gateway, or third-party SMS API that is not natively listed in On-Chat. This flexible integration method uses webhooks and API endpoints to route messages from your custom provider into On-Chat's shared inbox, giving your team full access to automation, routing, and reporting features.

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## Prerequisites
- An On-Chat account with admin access
- Access to your external SMS provider's API documentation
- API credentials from your SMS provider (API key, token, or username/password)
- Ability to configure webhook/callback URLs in your SMS provider
- Basic understanding of HTTP webhooks and API requests

## Step 1: Understand the External API Channel
On-Chat's External API channel acts as a universal SMS inbox connector. Your SMS provider sends inbound messages to On-Chat via a webhook URL, and On-Chat sends outbound replies back to your provider via its API. This two-way communication works with virtually any SMS gateway that supports webhooks and REST APIs.

## Step 2: Create an External API Inbox in On-Chat
In On-Chat, go to **Settings** → **Inboxes** → **New Inbox**. Select **API** or **External API** as the channel type. Give your inbox a descriptive name (e.g., "Custom SMS Gateway"). Save to generate your On-Chat **Webhook URL** and **API Access Token** — you will need these in the next steps.

## Step 3: Configure Inbound Messages from Your SMS Provider
In your SMS provider's dashboard, set the inbound message delivery URL to your On-Chat webhook endpoint. When a customer sends an SMS to your gateway number, your provider will POST the message payload to this URL. On-Chat will parse the payload and create a new conversation in the inbox.

## Step 4: Configure Outbound Messages via Your SMS Provider's API
In On-Chat, go to your External API inbox settings and add your SMS provider's outbound API endpoint, along with the required authentication headers or parameters (API key, auth token, etc.). On-Chat uses this configuration to send agent replies back to customers through your provider.

## Step 5: Map Incoming Message Fields
Ensure your SMS provider's inbound message payload includes the sender's phone number and message body in a format On-Chat can parse. Refer to On-Chat's External API documentation for the expected payload schema, and configure your provider's webhook to match the required format.

## Step 6: Assign Agents and Set Up Automation
In On-Chat, navigate to **Settings** → **Inboxes** → select your External API inbox → **Collaborators**. Add agents who will handle the conversations. Set up automation rules to route, tag, or auto-reply to messages as needed.

## Step 7: Test and Validate the Integration
Send a test message through your SMS gateway to trigger an inbound webhook event. Verify the message appears in your On-Chat External API inbox. Have an agent reply and confirm the reply is delivered back to the sender via your SMS provider's outbound API.

## Best Practices
- Document your SMS provider's payload format and store it in On-Chat's internal notes
- Use On-Chat's API logs to debug webhook delivery issues during setup
- Secure your webhook endpoint with token validation to prevent unauthorized message injection
- Test with multiple phone numbers to ensure bidirectional message flow works reliably

## Keep reading

- [How to Build a WhatsApp Chatbot Without Code](https://on-chat.live/guides/how-to-build-a-whatsapp-chatbot/): A step-by-step tutorial for building a dynamic WhatsApp chatbot in a visual flow builder, from your first message to live data and agent handoff.
- [Chatbot Flow Design: 12 Best Practices](https://on-chat.live/guides/chatbot-flow-design-best-practices/): Practical rules for designing chatbot conversation flows that customers finish: branching, fallbacks, personalisation, handoff and testing.
- [Make Your Chatbot Dynamic with Webhooks](https://on-chat.live/guides/dynamic-chatbot-webhooks/): Connect your chatbot flows to live data. Learn how webhooks, expressions and splits turn a scripted bot into one that answers with real information.