# MSG91 Send OTP API Documentation Summary

## Overview
MSG91 provides an OTP service that allows sending One-Time Passwords (OTPs) via SMS, WhatsApp, and Voice calls. Channel selection and fallback behavior are configured inside the OTP Template created in the MSG91 control panel.

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## 1. Send OTP Endpoint
- **URL**: `https://control.msg91.com/api/v5/otp`
- **HTTP Method**: `POST`

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## 2. Headers
| Header Name | Type | Required | Description |
|---|---|---|---|
| `authkey` | String | Yes | User authentication key (unique for every MSG91 user account). Can also be passed as query parameter. |
| `content-type` | String | Yes | `application/json` (when passing JSON payload for template parameters). |

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## 3. Query Parameters

### Required Parameters
| Parameter | Type | Description |
|---|---|---|
| `template_id` | String | OTP Template ID generated in the MSG91 Dashboard (OTP section). Configures the message template and delivery channels (SMS, WhatsApp, Voice). |
| `mobile` | String | Recipient mobile number in international format with country code (e.g. `919876543210`). |
| `authkey` | String | User authentication key. |

### Optional Parameters
| Parameter | Type | Default | Description |
|---|---|---|---|
| `otp` | String / Integer | Auto-generated | Custom OTP value to send. If omitted, MSG91 generates the OTP automatically. |
| `unicode` | Integer | `0` | Pass `1` for non-English SMS content, `0` for English. |
| `invisible` | Integer | `0` | Mobile App verification (1 = ON, 0 = OFF). Auto-verifies if mobile network is ON. |
| `otp_expiry` | Integer | `15` | OTP expiry in minutes (Min: 1 min, Max: 10080 mins / 7 days). |
| `otp_length` | Integer | `4` | Number of digits in generated OTP (Min: 4, Max: 9). |
| `realTimeResponse` | Integer | - | Pass `1` to receive real-time API response handling error codes via caching. |

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## 4. Request Body Parameters (JSON)
- **Content-Type**: `application/json`
- Pass dynamic variables defined in your MSG91 OTP template as JSON key-value pairs.
- Variable names are **case-sensitive**.

**Example JSON Payload**:
```json
{
  "Param1": "Value1",
  "Param2": "Value2",
  "company_name": "MyCompany"
}
```

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## 5. WhatsApp & Multi-Channel OTP Setup
- **Template-Based Routing**: Delivery channels (SMS vs WhatsApp) are configured within the MSG91 Dashboard under the OTP Template (`template_id`).
- When creating or editing an OTP template in MSG91, you can set WhatsApp as the primary or secondary fallback channel.
- **Resend OTP API**:
  - **Endpoint**: `GET https://control.msg91.com/api/v5/otp/retry`
  - **Query Parameters**:
    - `mobile`: Mobile number in international format.
    - `authkey`: User authentication key.
    - `retrytype`: Delivery type for resending OTP (`text` for SMS/WhatsApp text, `voice` for voice call; Default: `voice`).