Pre-class slide carousel in a WhatsApp group with the WhatsApp API

Q: Where are slide images prepared?

On your backend. The catalog Whapi step is only sendMessageCarousel. Scheduling, LMS export, and public HTTPS URLs for JPEGs stay in own_backend.

Use case

When to use this flow

The trigger is shortly before a scheduled class

Use this flow when a scheduled job fires shortly before a class session starts, not when an unrelated business event produces a one-off file.

The destination is an existing course group

Use this flow when each course already has a WhatsApp group JID and students should preview slides inside that group chat.

Slides go out as swipeable image cards

Use this flow when exported slide JPEGs should appear as one carousel students can swipe, not as a single document attachment or a weekly LMS chart report.

WhatsApp group chat on a phone showing a swipeable carousel of lecture slide images posted shortly before class.

Customer experience

Students preview slides in chat

Slide decks stay in the LMS or on the teacher's machine until someone manually posts in the course group, so students often open the chat without a swipeable preview on their phone.

After the flow runs, students open the course group and swipe through the lecture slides as a carousel before class starts. Integrators build this result with the WhatsApp API.

Workflow

Post the carousel into the group

The pre-class scheduler runs

Your scheduler fires shortly before the session. A worker reads LMS or calendar data, resolves the course group JID, and builds carousel cards from public HTTPS URLs for each slide JPEG.

Send the slide carousel to the course group

POST /messages/carousel

sendMessageCarousel delivers the card stack to the course group. Put the group JID in to and the card list in cards.

View code examples

Need delivery tracking? A successful API response does not mean students already see every slide card. Learn about delivery status →

Prerequisites

Before you run the flow

Connect the WhatsApp number that posts into course groups, and authenticate every request with that number's API token. The schedule, slide export, and carousel body stay on your backend.

1.Create a Whapi.Cloud account: Sign up
2.Connect your WhatsApp account: Open the guide
3.Find your API token: Open the section

Optional — go deeper for this flow

Automating WhatsApp groups: Open the guide
Send message with buttons: Open the guide
Sending messages overview: Open the guide

API implementation

One call sends the carousel

This call is the pre-class drop. It puts the compiled slide card stack into the course group chat so students can swipe before the session starts.

Get your API token for free after you register on whapi.cloud, and use that token in the code instead of Your_Token from the examples.

Send the slide carousel to the course group

Send the lecture slide carousel to the mapped course group so students can preview slides on their phones before class.

curl --request POST \
     --url https://gate.whapi.cloud/messages/carousel \
     --header 'accept: application/json' \
     --header 'authorization: Bearer Your_Token' \
     --header 'content-type: application/json' \
     --data '
{
  "to": "[email protected]",
  "body": {
    "text": "Lecture slides for today's class \u2014 swipe to preview before we start."
  },
  "cards": [
    {
      "id": "slide-1",
      "text": "Slide 1 \u2014 Introduction",
      "media": {
        "media": "https://cdn.example.com/courses/cs101/slides/slide-01.jpg"
      },
      "buttons": [
        {
          "type": "quick_reply",
          "title": "Next",
          "id": "next-1"
        }
      ]
    },
    {
      "id": "slide-2",
      "text": "Slide 2 \u2014 Key concepts",
      "media": {
        "media": "https://cdn.example.com/courses/cs101/slides/slide-02.jpg"
      },
      "buttons": [
        {
          "type": "quick_reply",
          "title": "Next",
          "id": "next-2"
        }
      ]
    },
    {
      "id": "slide-3",
      "text": "Slide 3 \u2014 Summary",
      "media": {
        "media": "https://cdn.example.com/courses/cs101/slides/slide-03.jpg"
      },
      "buttons": [
        {
          "type": "url",
          "title": "Open LMS",
          "id": "lms-1",
          "url": "https://lms.example.com/cs101"
        }
      ]
    }
  ]
}
'

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://gate.whapi.cloud/messages/carousel",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_CUSTOMREQUEST => "POST",
  CURLOPT_POSTFIELDS => "{\"to\":\"[email protected]\",\"body\":{\"text\":\"Lecture slides for today's class \\u2014 swipe to preview before we start.\"},\"cards\":[{\"id\":\"slide-1\",\"text\":\"Slide 1 \\u2014 Introduction\",\"media\":{\"media\":\"https://cdn.example.com/courses/cs101/slides/slide-01.jpg\"},\"buttons\":[{\"type\":\"quick_reply\",\"title\":\"Next\",\"id\":\"next-1\"}]},{\"id\":\"slide-2\",\"text\":\"Slide 2 \\u2014 Key concepts\",\"media\":{\"media\":\"https://cdn.example.com/courses/cs101/slides/slide-02.jpg\"},\"buttons\":[{\"type\":\"quick_reply\",\"title\":\"Next\",\"id\":\"next-2\"}]},{\"id\":\"slide-3\",\"text\":\"Slide 3 \\u2014 Summary\",\"media\":{\"media\":\"https://cdn.example.com/courses/cs101/slides/slide-03.jpg\"},\"buttons\":[{\"type\":\"url\",\"title\":\"Open LMS\",\"id\":\"lms-1\",\"url\":\"https://lms.example.com/cs101\"}]}]}",
  CURLOPT_HTTPHEADER => [
    "accept: application/json",
    "authorization: Bearer Your_Token",
    "content-type: application/json"
  ],
]);

$response = curl_exec($curl);
curl_close($curl);
echo $response;

import requests

url = "https://gate.whapi.cloud/messages/carousel"
payload = {
    "to": "[email protected]",
    "body": {
        "text": "Lecture slides for today's class \u2014 swipe to preview before we start."
    },
    "cards": [
        {
            "id": "slide-1",
            "text": "Slide 1 \u2014 Introduction",
            "media": {
                "media": "https://cdn.example.com/courses/cs101/slides/slide-01.jpg"
            },
            "buttons": [
                {
                    "type": "quick_reply",
                    "title": "Next",
                    "id": "next-1"
                }
            ]
        },
        {
            "id": "slide-2",
            "text": "Slide 2 \u2014 Key concepts",
            "media": {
                "media": "https://cdn.example.com/courses/cs101/slides/slide-02.jpg"
            },
            "buttons": [
                {
                    "type": "quick_reply",
                    "title": "Next",
                    "id": "next-2"
                }
            ]
        },
        {
            "id": "slide-3",
            "text": "Slide 3 \u2014 Summary",
            "media": {
                "media": "https://cdn.example.com/courses/cs101/slides/slide-03.jpg"
            },
            "buttons": [
                {
                    "type": "url",
                    "title": "Open LMS",
                    "id": "lms-1",
                    "url": "https://lms.example.com/cs101"
                }
            ]
        }
    ]
}
headers = {
    "accept": "application/json",
    "authorization": "Bearer Your_Token",
    "content-type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)
print(response.text)

const response = await fetch('https://gate.whapi.cloud/messages/carousel', {
  method: 'POST',
  headers: {
    accept: 'application/json',
    authorization: 'Bearer Your_Token',
    'content-type': 'application/json',
  },
  body: JSON.stringify({
    "to": "[email protected]",
    "body": {
      "text": "Lecture slides for today's class \u2014 swipe to preview before we start."
    },
    "cards": [
      {
        "id": "slide-1",
        "text": "Slide 1 \u2014 Introduction",
        "media": {
          "media": "https://cdn.example.com/courses/cs101/slides/slide-01.jpg"
        },
        "buttons": [
          {
            "type": "quick_reply",
            "title": "Next",
            "id": "next-1"
          }
        ]
      },
      {
        "id": "slide-2",
        "text": "Slide 2 \u2014 Key concepts",
        "media": {
          "media": "https://cdn.example.com/courses/cs101/slides/slide-02.jpg"
        },
        "buttons": [
          {
            "type": "quick_reply",
            "title": "Next",
            "id": "next-2"
          }
        ]
      },
      {
        "id": "slide-3",
        "text": "Slide 3 \u2014 Summary",
        "media": {
          "media": "https://cdn.example.com/courses/cs101/slides/slide-03.jpg"
        },
        "buttons": [
          {
            "type": "url",
            "title": "Open LMS",
            "id": "lms-1",
            "url": "https://lms.example.com/cs101"
          }
        ]
      }
    ]
  }),
});

console.log(await response.text());

OkHttpClient client = new OkHttpClient();

MediaType mediaType = MediaType.parse("application/json");
RequestBody body = RequestBody.create(mediaType, "{\"to\":\"[email protected]\",\"body\":{\"text\":\"Lecture slides for today's class \\u2014 swipe to preview before we start.\"},\"cards\":[{\"id\":\"slide-1\",\"text\":\"Slide 1 \\u2014 Introduction\",\"media\":{\"media\":\"https://cdn.example.com/courses/cs101/slides/slide-01.jpg\"},\"buttons\":[{\"type\":\"quick_reply\",\"title\":\"Next\",\"id\":\"next-1\"}]},{\"id\":\"slide-2\",\"text\":\"Slide 2 \\u2014 Key concepts\",\"media\":{\"media\":\"https://cdn.example.com/courses/cs101/slides/slide-02.jpg\"},\"buttons\":[{\"type\":\"quick_reply\",\"title\":\"Next\",\"id\":\"next-2\"}]},{\"id\":\"slide-3\",\"text\":\"Slide 3 \\u2014 Summary\",\"media\":{\"media\":\"https://cdn.example.com/courses/cs101/slides/slide-03.jpg\"},\"buttons\":[{\"type\":\"url\",\"title\":\"Open LMS\",\"id\":\"lms-1\",\"url\":\"https://lms.example.com/cs101\"}]}]}");
Request request = new Request.Builder()
  .url("https://gate.whapi.cloud/messages/carousel")
  .post(body)
  .addHeader("accept", "application/json")
  .addHeader("authorization", "Bearer Your_Token")
  .addHeader("content-type", "application/json")
  .build();

Response response = client.newCall(request).execute();

using RestSharp;

var options = new RestClientOptions("https://gate.whapi.cloud/messages/carousel");
var client = new RestClient(options);
var request = new RestRequest("");
request.AddHeader("accept", "application/json");
request.AddHeader("authorization", "Bearer Your_Token");
request.AddHeader("content-type", "application/json");
request.AddJsonBody({"to":"[email protected]","body":{"text":"Lecture slides for today's class \u2014 swipe to preview before we start."},"cards":[{"id":"slide-1","text":"Slide 1 \u2014 Introduction","media":{"media":"https://cdn.example.com/courses/cs101/slides/slide-01.jpg"},"buttons":[{"type":"quick_reply","title":"Next","id":"next-1"}]},{"id":"slide-2","text":"Slide 2 \u2014 Key concepts","media":{"media":"https://cdn.example.com/courses/cs101/slides/slide-02.jpg"},"buttons":[{"type":"quick_reply","title":"Next","id":"next-2"}]},{"id":"slide-3","text":"Slide 3 \u2014 Summary","media":{"media":"https://cdn.example.com/courses/cs101/slides/slide-03.jpg"},"buttons":[{"type":"url","title":"Open LMS","id":"lms-1","url":"https://lms.example.com/cs101"}]}]});
var response = await client.PostAsync(request);

Console.WriteLine("{0}", response.Content);

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
)

func main() {
	body := []byte(`{"to":"[email protected]","body":{"text":"Lecture slides for today's class \u2014 swipe to preview before we start."},"cards":[{"id":"slide-1","text":"Slide 1 \u2014 Introduction","media":{"media":"https://cdn.example.com/courses/cs101/slides/slide-01.jpg"},"buttons":[{"type":"quick_reply","title":"Next","id":"next-1"}]},{"id":"slide-2","text":"Slide 2 \u2014 Key concepts","media":{"media":"https://cdn.example.com/courses/cs101/slides/slide-02.jpg"},"buttons":[{"type":"quick_reply","title":"Next","id":"next-2"}]},{"id":"slide-3","text":"Slide 3 \u2014 Summary","media":{"media":"https://cdn.example.com/courses/cs101/slides/slide-03.jpg"},"buttons":[{"type":"url","title":"Open LMS","id":"lms-1","url":"https://lms.example.com/cs101"}]}]}`)
	req, _ := http.NewRequest("POST", "https://gate.whapi.cloud/messages/carousel", bytes.NewReader(body))
	req.Header.Set("accept", "application/json")
	req.Header.Set("authorization", "Bearer Your_Token")
	req.Header.Set("content-type", "application/json")

	res, _ := http.DefaultClient.Do(req)
	defer res.Body.Close()
	out, _ := io.ReadAll(res.Body)
	fmt.Println(string(out))
}

Get API KEY for free

Delivery

Know when the carousel arrived

A successful send response does not mean students already received the carousel. The first status visible before a webhook is pending. Later status changes arrive only on statuses.post and statuses.put. If the status stays pending and does not move to sent, delivered, or a later ack, the message was not delivered. Check the payload and the account's permission to send that type.

A response from sendMessageCarousel is not proof students see the slides.
pending that never moves on means the carousel was not delivered.
Watch statuses.post and statuses.put for later acks.
Enable webhooks if your worker should retry when delivery never completes.

What to read on delivery and webhooks

What a delivered webhook looks like: See the callback
Which events we send to a webhook: See tracked events
How to set a webhook on a channel: Open the guide
Where to get the webhook URL: Open the guide
Webhook payload examples: See the formats

Contact our support if something went wrong

When things break

Handle failures at each step

If the course group JID is wrong, slide image URLs are missing, the carousel send is rejected or not delivered, or carousel support is temporarily unavailable, fix the target or assets, retry or fall back, and do not treat the pre-class drop as done.

Scheduler ran, but the drop failed?

The group JID can be wrong, slide URLs can be missing, or sendMessageCarousel can be rejected or not delivered after the cards were ready. Retry the worker, fall back to a single image or document post if carousel support fails, and do not treat the pre-class drop as done. If the drop still fails after a retry, contact Whapi support with the channel id and the failed send response.

Contact our support if something went wrong

Troubleshoot by API step

Status	What it means	What to do
`400`	Wrong request parameters	Wrong request parameters — check `to`, `cards`, and carousel body fields on the send payload.
`401`	Need channel authorization for send message
`402`	Trial version limit exceeded
`403`	It is forbidden to send to this group/recipient	It is forbidden to send to this group — confirm the course group JID and channel permissions.
`404`	Media with specified id not found	Media with specified id not found — confirm each card media URL or id resolves before send.
`413`	Request media too large
`415`	Unsupported media type
`429`	Too many requests
`500`	Internal Error

FAQ

Questions integrators ask

No. This flow posts slide JPEGs as one carousel shortly before a scheduled class. A generic file drop on an unrelated business event uses a document send and a different trigger.

No. This flow targets students in a course group before one class. Weekly visual reports broken down by class or teacher are a separate scheduled report scenario.

If the course group JID is wrong, slide URLs are missing, the send is rejected or not delivered, or carousel support is temporarily unavailable, fix the target or assets, retry or fall back, and do not treat the pre-class drop as done.

On your backend. The catalog Whapi step is only sendMessageCarousel. Scheduling, LMS export, and public HTTPS URLs for JPEGs stay in own_backend.

No. You build the carousel body from your slide URLs and send it with sendMessageCarousel. Carousel and button availability can change with WhatsApp updates; plan a fallback send path if support is unavailable.

Get started with the API

Supported WhatsApp Features

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When to use this flow

Students preview slides in chat

Post the carousel into the group

Before you run the flow

One call sends the carousel

Send the slide carousel to the course group

Know when the carousel arrived

What to read on delivery and webhooks

Handle failures at each step

Troubleshoot by API step

Send the slide carousel to the course group sendMessageCarousel · POST /messages/carousel

Questions integrators ask

Is this the same as sending a file to a group on a business event?

Is this the weekly visual LMS upload report?

What if students never see the carousel?

Where are slide images prepared?

Do I need a pre-approved message template for the slides?

Everything you need to build WhatsApp automation

WhatsApp Channels API

WhatsApp Groups & Communities

No templates or approvals

Real-time webhooks

All Media & Message Types

Orders & product automation

WhatsApp number validation

Low-code & no-code friendly

WhatsApp Statuses API

Delivery & read status

Multi-device connection

Interactive messages & buttons

Trusted by 3,300+ developers and SaaS teams

5,5K+

21M+

“Everything is simple, intuitive and easy to navigate. The docs are clear, and all the info I need is right on the screen. Great job.”

“We connected WhatsApp to our workflows using n8n in just a few minutes. No code, no complications- everything worked on the first try.”

“Whapi.Cloud became a key part of our customer communication. We automated product updates, order notifications and support messages without needing Meta templates or approvals”

Guides next to this