Protocol Selection

The Linq API supports sending messages via iMessage, RCS, and SMS. You can let the API automatically select the best protocol or explicitly choose one. See the Create Chat API reference for the full specification.

Automatic selection (default)

When preferred_service is omitted, the API uses the full fallback chain: iMessage → RCS → SMS.

Explicit protocol selection

Use preferred_service inside the message object to control which protocol is used:

Value	Behavior
iMessage	iMessage only. No fallback — send fails if the recipient is unavailable on iMessage.
RCS	RCS if supported, otherwise SMS. Never uses iMessage.
SMS	RCS if supported, otherwise SMS. Never uses iMessage.

preferred_service vs service: preferred_service is what you requested. The service field on the response is what was actually used for delivery.

curl -X POST https://api.linqapp.com/api/partner/v3/chats \
  -H "Authorization: Bearer $LINQ_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "+12223334444",
    "to": ["+15556667777"],
    "message": {
      "preferred_service": "iMessage",
      "parts": [
        { "type": "text", "value": "This will be sent via iMessage" }
      ]
    }
  }'

const chat = await client.chats.create({
  from: '+12223334444',
  to: ['+15556667777'],
  message: {
    preferred_service: 'iMessage',
    parts: [{ type: 'text', value: 'This will be sent via iMessage' }],
  },
});

chat = client.chats.create(
    from_="+12223334444",
    to=["+15556667777"],
    message={
        "preferred_service": "iMessage",
        "parts": [{"type": "text", "value": "This will be sent via iMessage"}],
    },
)

Protocol capabilities

Not all features are available on every protocol:

Feature	iMessage	RCS	SMS
Text messages	Yes	Yes	Yes
Images & video	Yes	Yes	MMS
Read receipts	Yes	Yes	No
Delivery receipts	Yes	Yes	No
Typing indicators	Yes	No	No
Reactions / tapbacks	Yes	Yes	No
Message effects	Yes	No	No
Group chats	Yes	Yes	MMS
Message threading	Yes	No	No
Rich link previews	Yes	Yes	No
Voice memos	Yes	Yes	No
File attachments (100MB)	Yes	Limited	No
Text decorations	Yes	No	No

When to choose a protocol

• iMessage — When you need Apple-exclusive features like message effects or text decorations. Be aware: delivery fails if the recipient isn’t on iMessage.
• RCS — When you want rich messaging on Android (reactions, read receipts, threading) but still want SMS as a fallback.
• SMS — Equivalent to RCS in behavior: uses RCS if supported, otherwise SMS. Never iMessage.
• Omit — Best for maximum reach. The API picks the richest available protocol automatically.

Note: Use the capability check endpoints to verify recipient support before specifying iMessage. See Capability Checks for details.