> ## Documentation Index
> Fetch the complete documentation index at: https://docs.prelude.so/llms.txt
> Use this file to discover all available pages before exploring further.
# Reply to an inbound message
> Send a free-form text reply to an inbound WhatsApp message within the 24-hour conversation window.
```javascript Node.js theme={null}
import Prelude from "@prelude.so/sdk";
const client = new Prelude();
async function main() {
const response = await client.notify.reply({
to: "+33612345678",
text: "Thanks for reaching out! We'll look into your request.",
reply_to: "im_01k8aq2zggeyssvt53zgvpx63a",
});
console.log(response.id);
}
main();
```
```go Go theme={null}
package main
import (
"context"
"fmt"
"github.com/prelude-so/go-sdk"
"github.com/prelude-so/go-sdk/option"
)
func main() {
client := prelude.NewClient()
response, err := client.Notify.Reply(context.TODO(), prelude.NotifyReplyParams{
To: prelude.F("+33612345678"),
Text: prelude.F("Thanks for reaching out! We'll look into your request."),
ReplyTo: prelude.F("im_01k8aq2zggeyssvt53zgvpx63a"),
})
if err != nil {
panic(err.Error())
}
fmt.Printf("%+v\n", response.ID)
}
```
```python Python theme={null}
import os
from prelude_python_sdk import Prelude
client = Prelude()
response = client.notify.reply(
to="+33612345678",
text="Thanks for reaching out! We'll look into your request.",
reply_to="im_01k8aq2zggeyssvt53zgvpx63a",
)
print(response.id)
```
Replies are delivered as native WhatsApp quoted messages and must be sent within the **24-hour conversation window** that follows the latest inbound message from the same user. See [WhatsApp 2-Way Messaging](/notify/v2/documentation/whatsapp) for the full flow.
## Request fields
The recipient's phone number in E.164 format. Must match the phone number that sent the original inbound message — otherwise a `phone_number_mismatch` error is returned.
The reply message body. Sent as a free-form WhatsApp text, not as a template.
The inbound message ID (prefixed with `im_`) to reply to. This ID is provided in the `inbound.message.received` webhook event.
The URL where webhooks will be sent for delivery events of this reply.
A user-defined identifier to correlate this reply with your internal systems. It is returned in the response and any webhook events that refer to this message.
## Error Handling
The reply endpoint returns specific error codes for 2-way messaging failures:
| Error Code | Description | Action |
| ----------------------- | --------------------------------------------------------- | -------------------------------------------------------------------------------------------------- |
| `window_expired` | The 24-hour WhatsApp conversation window has closed | Use a template-based message via [Send a message](/notify/v2/api-reference/send-a-message) instead |
| `invalid_reply_context` | The inbound message ID in `reply_to` was not found | Verify the message ID from the `inbound.message.received` webhook |
| `phone_number_mismatch` | The `to` number does not match the inbound message sender | Use the phone number from the inbound webhook |
| `missing_text` | The `text` field is empty | Provide a reply message body |
| `invalid_phone_number` | Phone number format is invalid | Validate phone number format |
| `insufficient_balance` | Account balance is too low | Top up your account |
For a complete list of errors, see the [Error documentation](/introduction/errors).
## Related Documentation
* [WhatsApp 2-Way Messaging](/notify/v2/documentation/whatsapp) - Receive inbound messages and send replies
* [Send a message](/notify/v2/api-reference/send-a-message) - Send templated transactional and marketing messages
* [Webhooks](/notify/v2/documentation/webhook) - Receive delivery updates, inbound messages, and subscription events
## OpenAPI
````yaml post /v2/notify/reply
openapi: 3.1.0
info:
title: Prelude API
version: 2.0.0
description: The Prelude API allows you to send messages to your users.
contact:
email: support@prelude.so
servers:
- url: https://api.prelude.dev
description: Production server
security:
- apiToken: []
tags:
- name: Notify
description: Send transactional and marketing messages with compliance enforcement.
- name: Transactional
description: Send transactional messages (deprecated - use Notify API instead).
- name: Verify
description: Verify phone numbers.
- name: Watch
description: Evaluate email addresses and phone numbers for trustworthiness.
- name: Lookup
description: >-
Retrieve detailed information about a phone number including carrier data,
line type, and portability status.
paths:
/v2/notify/reply:
post:
tags:
- Notify
summary: Reply to an inbound message
description: >-
Send a free-form text reply to an inbound WhatsApp message within the
24-hour conversation window. See [WhatsApp 2-Way
Messaging](/notify/v2/documentation/whatsapp) for details.
operationId: sendNotifyReply
requestBody:
required: true
content:
application/json:
schema:
$ref: '#/components/schemas/SendNotifyReplyRequest'
responses:
'200':
description: OK
content:
application/json:
schema:
$ref: '#/components/schemas/SendNotifyReplyResponse'
'400':
description: KO
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
callbacks:
webhook_event:
'{$request.body#/callback_url}':
post:
requestBody:
required: true
content:
application/json:
schema:
$ref: '#/components/schemas/WebhookEvent'
responses:
'200':
description: Your server accepted the event and will process it.
default:
description: >-
Your server did not accept the event and we will retry for
24 hours.
components:
schemas:
SendNotifyReplyRequest:
type: object
properties:
to:
type: string
description: >-
The recipient's phone number in E.164 format. Must match the phone
number that sent the original inbound message.
examples:
- '+33612345678'
text:
type: string
description: The reply message body sent as a free-form WhatsApp text.
examples:
- Thanks for reaching out! We'll look into your request.
reply_to:
type: string
description: >-
The inbound message ID (prefixed with `im_`) to reply to. This ID is
provided in the `inbound.message.received` webhook event.
examples:
- im_01k8aq2zggeyssvt53zgvpx63a
callback_url:
type: string
description: >-
The URL where webhooks will be sent for delivery events of this
reply.
examples:
- https://your-app.com/webhooks/notify
correlation_id:
type: string
description: >-
A user-defined identifier to correlate this reply with your internal
systems. It is returned in the response and any webhook events that
refer to this message.
maxLength: 80
examples:
- support-ticket-42
required:
- to
- text
- reply_to
SendNotifyReplyResponse:
type: object
properties:
id:
type: string
description: The reply message identifier.
examples:
- tx_01k8ap1btqf5r9fq2c8ax5fhc9
to:
type: string
description: The recipient's phone number in E.164 format.
examples:
- '+33612345678'
text:
type: string
description: The reply message body that was sent.
examples:
- Thanks for reaching out! We'll look into your request.
reply_to:
type: string
description: The inbound message ID this reply was sent in response to.
examples:
- im_01k8aq2zggeyssvt53zgvpx63a
callback_url:
type: string
description: The callback URL where webhooks will be sent.
examples:
- https://your-app.com/webhooks/notify
correlation_id:
type: string
description: >-
The user-defined correlation identifier echoed back from the
request.
maxLength: 80
examples:
- support-ticket-42
created_at:
type: string
format: date-time
description: The reply creation date in RFC3339 format.
examples:
- '2025-10-24T12:00:00Z'
required:
- id
- to
- text
- reply_to
- created_at
Error:
type: object
properties:
code:
type: string
description: The error code.
examples:
- invalid_phone_number
message:
type: string
examples:
- >-
The provided phone number is invalid. Provide a valid E.164 phone
number.
description: A human-readable message describing the error.
type:
type: string
examples:
- bad_request
description: The error type.
request_id:
type: string
examples:
- 3d19215e-2991-4a05-a41a-527314e6ff6a
description: >-
A string that identifies this specific request. Report it back to us
to help us diagnose your issues.
required:
- code
- message
- type
securitySchemes:
apiToken:
type: http
scheme: bearer
````