Connect Google Calendar to WhatsApp

Use case 1 (WA.Expert calls Google): customer books on WhatsApp, automation creates a Calendar event. Use case 2 (Google calls WA.Expert): upcoming event triggers a WhatsApp reminder. Both are covered in this guide.

Creating or reading Calendar events via the Google Calendar API requires an OAuth access token, not a plain API key. The simplest path for both use cases is Apps Script, which runs as your own Google account and has calendar access without any token exchange in WA.Expert.

function doPost(e) {{
  var data  = JSON.parse(e.postData.contents);
  var cal   = CalendarApp.getDefaultCalendar();

  // Parse start time from ISO string, e.g. '2026-06-25T10:00:00'
  var start = new Date(data.start_datetime);
  var end   = new Date(data.end_datetime);

  var options = {{
    description: data.description || '',
    guests:      data.customer_email || '',
    sendInvites: true
  }};

  var event = cal.createEvent(
    data.title,
    start,
    end,
    options
  );

  return ContentService
    .createTextOutput(JSON.stringify({{
      status:   'ok',
      event_id: event.getId(),
      link:     event.getEventSeriesId()
    }}))
    .setMimeType(ContentService.MimeType.JSON);
}}

Body:
{{
  "title":           "Consultation: Priya Sharma",
  "start_datetime":  "2026-06-25T10:00:00",
  "end_datetime":    "2026-06-25T10:30:00",
  "description":     "WhatsApp booking — product demo request",
  "customer_email":  "priya@example.com"
}}

Response:
{{"status": "ok", "event_id": "abc123_2026062510@google.com"}}

"The event appears in your Google Calendar immediately.
The customer receives a Google Calendar invite if customer_email is provided.

Pass dates as ISO 8601 strings: 2026-06-25T10:00:00. The script parses them with new Date(). Collect the slot from the customer in WhatsApp as a variable, or build the string from separate date and time variables: {{slot_date}}T{{slot_time}}:00.

var WA_WEBHOOK = 'YOUR_WA_EXPERT_WEBHOOK_URL';

function sendReminders() {{
  var cal      = CalendarApp.getDefaultCalendar();
  var tomorrow = new Date();
  tomorrow.setDate(tomorrow.getDate() + 1);

  var events = cal.getEventsForDay(tomorrow);

  events.forEach(function(event) {{
    var desc  = event.getDescription();
    // Extract phone from description (e.g. 'phone:+919820000001')
    var match = desc.match(/phone:([\+0-9]+)/);
    if (!match) return;

    var payload = {{
      phone:     match[1],
      title:     event.getTitle(),
      startTime: event.getStartTime().toLocaleString('en-IN'),
      location:  event.getLocation() || 'your scheduled session'
    }};

    UrlFetchApp.fetch(WA_WEBHOOK, {{
      method:      'post',
      contentType: 'application/json',
      payload:     JSON.stringify(payload)
    }});
  }});
}}

// Add a time-driven trigger: Triggers -> Add Trigger
// sendReminders -> Time-driven -> Day timer -> 8am-9am

When creating the event (Use case 1), include the customer's WhatsApp number in the event description using a parseable format like phone:+919820000001. The reminder script then extracts it with a regex and sends the reminder to the right number.

POST https://www.googleapis.com/calendar/v3/calendars/primary/events
     ?sendUpdates=all
Authorization: Bearer YOUR_OAUTH_ACCESS_TOKEN
Content-Type: application/json

Body:
{{
  "summary":     "Consultation: Priya Sharma",
  "description": "WhatsApp booking",
  "start": {{"dateTime": "2026-06-25T10:00:00+05:30",
             "timeZone": "Asia/Kolkata"}},
  "end":   {{"dateTime": "2026-06-25T10:30:00+05:30",
             "timeZone": "Asia/Kolkata"}},
  "attendees": [{{"email": "priya@example.com"}}]
}}

Response (HTTP 200):
{{
  "kind":    "calendar#event",
  "id":      "abc123",
  "htmlLink":"https://calendar.google.com/calendar/event?eid=...",
  "status":  "confirmed"
}}

Map: id -> event_id, htmlLink -> calendar_link

Customer: 'I want to book a consultation'

Bot collects:
  {{customer_name}}  = Priya Sharma
  {{customer_email}} = priya@example.com
  {{slot_date}}      = 2026-06-25
  {{slot_time}}      = 10:00

External API Request step:
POST https://script.google.com/macros/s/AKfy.../exec
Body:
  title:           'Consultation: Priya Sharma'
  start_datetime:  '2026-06-25T10:00:00'
  end_datetime:    '2026-06-25T10:30:00'
  description:     'phone:+919820000001'
  customer_email:  'priya@example.com'

Response: {{status: 'ok', event_id: '...'}}

WA.Expert replies to Priya:
'Your appointment is confirmed for 25 June at 10:00 AM.
You will receive a reminder on WhatsApp the day before.
See you then!'

Next morning (8 AM), the daily reminder script fires:
  Reads tomorrow's event for Priya
  Extracts phone from description: +919820000001
  Posts to WA.Expert webhook

WA.Expert sends Priya:
'Reminder: your consultation is tomorrow at 10:00 AM.
Reply CONFIRM to confirm or CANCEL to reschedule.'