RCS API Overview: Send, Receive, and Webhooks

Quick answer

The RCS API is a REST interface for sending RCS messages from a verified agent and receiving user interactions via webhooks. You authenticate, check a number’s RCS capability, then POST a message (text, rich card, or carousel with suggestions) to a send endpoint addressed by your agent ID; inbound replies, taps, read receipts, and delivery events arrive at your configured webhook. With SimplyRCS, the same capabilities are available via API and the app at the same price, with SMS/MMS fallback handled automatically.

A typical send is an HTTPS POST with a JSON body describing the message. Following Google RBM conventions, a minimal text send looks like this (endpoint and IDs simplified):

POST https://{region}-rcsbusinessmessaging.googleapis.com/v1/phones/{E164_PHONE}/agentMessages?agentId={AGENT_ID}
Content-Type: application/json

{
  "contentMessage": {
    "text": "Your order #1043 has shipped 📦",
    "suggestions": [
      { "action": { "text": "Track", "postbackData": "track_1043",
        "openUrlAction": { "url": "https://shop.example/track/1043" } } }
    ]
  }
}

Before sending, call the capability check for the destination; if it isn’t RCS-capable, send via SMS/MMS instead (a good provider does this fallback for you).

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