Hi everyone 👋

I’ve been testing an automation where n8n connects to the ManyChat API using an HTTP Request node to send a message via Facebook Messenger.
However, my request keeps failing with the following error:

400 - {"status":"error","message":"Validation error","details":{"messages":[{"message":"Subscriber does not exist"}]}}

🔧 Setup details:

• Platform: n8n Cloud

• Node: HTTP Request

• Method: POST

• URL: https://api.manychat.com/fb/sending/sendContent

• Headers:

  • Authorization: Bearer <my_page_access_token>

  • Content-Type: application/json

• Body (JSON):

{
  "subscriber_id": "{{ $('Webhook').item.json.body.contact_id }}",
  "data": {
    "version": "v2",
    "content": {
      "type": "messenger",
      "messages": [
        {
          "type": "text",
          "text": "Машаа Elite Pool Billiard Club-д урьж байна..."
        }
      ]
    }
  }
}

⚠️ What happens:

The workflow runs successfully until the HTTP Request node, where I get the 400 Validation error above.

I confirmed that the subscriber_id (e.g. 25193238166929150) is coming from ManyChat’s webhook payload, but the API says the subscriber doesn’t exist.

I also noticed from a ManyChat community post