Adds a new message to an existing conversation. The message can be sent by either
the contact or an account (team member).

Use Cases

1. Contact replies (customer responds)

When sender_type is "contact", the contact who owns the conversation is replying.

• Only the sender_type field is required (no account_id needed)
• The contact is automatically identified from the conversation
• AI chatflow may be triggered if configured

2. Account replies (team member responds)

When sender_type is "account", a team member is replying to the contact.

• Both sender_type and account_id are required
• The account must have permission to view this conversation
• The conversation must NOT be assigned to AI (Aura)
  • If assigned to AI, you'll get a conversation_assigned_to_ai error

Request Fields

Required fields

• sender_type (string): Who is sending - either "contact" or "account"
• At least one of: content or attachments must be provided

Conditional fields

• account_id (integer): Required only when sender_type is "account"

Optional fields

• content (string): Message text. HTML is supported (safe tags: p, br, b, i, u, a, img)
• attachments (array): File attachments (max 5 files, 5MB each)
• is_note (boolean): Mark message as internal note (default: false). Only available when sender_type is "account".
  Notes are visible only to team members, not to contacts.

Examples

Example 1: Contact replies

{
  "sender_type": "contact",
  "content": "<p>Thanks for the help!</p>"
}

Example 2: Account replies

{
  "sender_type": "account",
  "account_id": 456,
  "content": "<p>I'm glad I could help!</p>"
}

Example 3: Reply with attachment

{
  "sender_type": "contact",
  "content": "<p>Here's the document you requested</p>",
  "attachments": [
    {
      "filename": "invoice.pdf",
      "base64": "data:application/pdf;base64,JVBERi0..."
    }
  ]
}

Example 4: Account sends internal note

{
  "sender_type": "account",
  "account_id": 456,
  "content": "<p>Customer seems frustrated, handle with care</p>",
  "is_note": true
}