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.

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

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

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": "+12052535597",
      "to": [
        "+12052532136"
      ],
      "message": {
        "preferred_service": "iMessage",
        "parts": [
          {
            "type": "text",
            "value": "Sent via iMessage only"
          }
        ]
      }
    }'

await client.chats.create({
  from: "+12052535597",
  to: ["+12052532136"],
  message: {
    preferred_service: "iMessage",
    parts: [
      {
        type: "text",
        value: "Sent via iMessage only",
      },
    ],
  },
});

client.chats.create(
    from_="+12052535597",
    to=["+12052532136"],
    message={
        "preferred_service": "iMessage",
        "parts": [
            {
                "type": "text",
                "value": "Sent via iMessage only",
            },
        ],
    },
)

client.Chats.Create(context.TODO(), linq.ChatNewParams{
  From: linq.F("+12052535597"),
  To: linq.F([]string{"+12052532136"}),
  Message: linq.F(map[string]any{
    PreferredService: linq.F("iMessage"),
    Parts: linq.F([]any{
      map[string]any{
        Type: linq.F("text"),
        Value: linq.F("Sent via iMessage only"),
      },
    }),
  }),
})

Not all features are available on every protocol:

• iMessage — When you need iMessage-only 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.