Two-way & keywords

The inbound event

When a reply arrives on a sandbox virtual number, Fabric emits a message.inbound webhook event:

if (event.type === "message.inbound") {
  const { messageId, channel } = event.data; // InboundMessageWebhookData
  await handleReply(messageId, channel);
}

Verify the signature and dedupe on event.id exactly as you do for delivery events.

Keywords are handled for you

STOP, START, and HELP are consent keywords, and Fabric applies them automatically:

STOP opts the recipient out. Subsequent promotional sends to that number are suppressed.
START opts the recipient back in.
HELP triggers the help response.

You do not implement opt-out yourself — Fabric records it in the consent store so the send-path gate enforces it on your behalf. See compliance for how opt-out interacts with transactional vs promotional traffic.

Test it in sandbox

Send a sandbox message, then use the dashboard’s virtual phone to reply (including a STOP), and watch the message.inbound event reach your webhook while the opt-out takes effect on the next promotional send. This lets you build and verify your inbound handling before any live inbound route exists.