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SendiMessage
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Send SMS from Express with the SendiMessage API

Express covers both directions of a SendiMessage integration in a dozen lines with the official npm SDK: one route your systems call to send, and one route that receives delivery and reply webhooks.

The SDK ships verifyWebhookSignature, so the webhook route can check the timestamped SendiMessage-Signature header against the raw body before trusting any event.

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What this integration enables

Order and status notifications
Trigger messages from Express when records change state.
Appointment reminders
Scheduled tasks that message customers before a booking.
Support updates
Notify customers as their request moves forward.
Reply handling
Receive incoming replies on a webhook route in the same codebase.

Architecture

How it fits together: Your application event, then Express server code, then SendiMessage API, then Managed messaging line, then Webhook events.
  1. Your application eventAn order ships, a booking nears, a ticket updates
  2. Express server codeBuilds the request with credentials from the environment
  3. SendiMessage APIPOST /send-message returns the queued message
  4. Managed messaging lineSMS, or iMessage on supported lines and destinations
  5. Webhook eventsDelivery status and incoming replies post back to your endpoint

Example request

Express
// npm install sendimessage
import express from "express";
import SendImessage, { verifyWebhookSignature } from "sendimessage";


const app = express();
const client = new SendImessage({
  apiKey: process.env.SENDIMESSAGE_KEY,
  apiSecret: process.env.SENDIMESSAGE_SECRET,
});


// Outbound: your systems call this to send.
app.post("/notify", express.json(), async (req, res) => {
  try {
    const msg = await client.sendMessage({ number: req.body.to, content: req.body.content });
    res.json({ handle: msg.message_handle, status: msg.status }); // "QUEUED"
  } catch (err) {
    res.status(502).json({ error: String(err) });
  }
});


// Inbound: SendiMessage posts delivery + reply events here.
// Raw body required — re-serialized JSON differs byte-for-byte.
app.post("/webhooks/sendimessage", express.raw({ type: "application/json" }), (req, res) => {
  const ok = verifyWebhookSignature({
    secret: process.env.WEBHOOK_SECRET,
    rawBody: req.body,
    signatureHeader: req.get("SendiMessage-Signature") ?? "", // "t=...,v1=..."
  });
  if (!ok) return res.sendStatus(401);


  const event = JSON.parse(req.body); // event.type: "outbound" | "receive" | line events
  res.sendStatus(200);
});


app.listen(3000);

Delivery events and incoming replies

Point a Express route at your webhook URL to receive delivery status and incoming replies. Verify the signature header before processing.

webhook event
// "outbound" event → your express endpoint
// Verify the SendiMessage-Signature header (t={timestamp},v1=HMAC-SHA256 of
// "{timestamp}.{raw body}", keyed with your webhook secret), then use
// GET /v2/messages/{message_handle} for authoritative state and match it to
// your contact_id in express.

Limitations and honest notes

  • iMessage delivery is available on supported messaging lines and destinations. Recipients without iMessage receive SMS when fallback is configured — never assume universal iMessage availability.
  • Messages are accepted asynchronously — the API returns status QUEUED and final status arrives via webhook or the message endpoints.
  • Official SDKs are published for JavaScript/TypeScript (npm: sendimessage), Python (PyPI: sendimessage), PHP (Composer: sendimessage/sdk), and Go (github.com/sendimessage/sendimessage-go). Every SDK is dependency-free and covers the full public API surface.

Security considerations

  • Keep the API key pair in server configuration or environment variables, never in the repository.
  • Verify webhook signatures before trusting delivery or reply events.

Frequently asked questions

Is there an official Express package for SendiMessage?
The official SDK for this ecosystem works in any Express project — install it with `npm install sendimessage`. It is dependency-free, covers the full public API, and ships a webhook signature verification helper.
Can Express receive message replies?
Yes. Add a route that accepts SendiMessage webhook POSTs; incoming replies arrive as receive events. Correlate them with your records via the message_handle and conversation data in the event.

Ready to connect Express?

Request a messaging line and a SendiMessage integration specialist will review your Express workflow and guide the setup.