SMS

SMS runs on Telnyx or Infobip and answers with AI by default. You pick the provider when you connect the channel — there is no default, so choose the one you have an account with. (There is no Twilio integration; the platform's two phone providers are Telnyx and Infobip, and they also power Voice and the provider routes for WhatsApp.)

How the channel works

Before the steps, the mental model — it makes every later section obvious:

1. 1
   Connecting the channel stores your provider credentials encrypted and gives you one inbound webhook URL of the form https://…/api/channels/{channelId}/inbound. That URL is unique to this channel.
2. 2
   You point your provider's inbound-message webhook at that URL. From then on, every text to your number is POSTed there.
3. 3
   The platform verifies each POST (Ed25519 signature for Telnyx, a URL secret for Infobip), turns it into a message in a conversation, and — with AI replies on — answers through the same retrieval pipeline as the widget.
4. 4
   Delivery receipts for your outbound replies arrive on the same webhook URL and are synced onto each reply's row in the console.

One number maps to one webhook slot, so one number belongs to one channel. The platform warns you if you try to connect a number that another chatbot already uses (see Duplicate numbers).

What you need

A messaging-capable number from one provider:

• Telnyx — an SMS-capable number, your API key, and the account's public key (the Ed25519 key Telnyx signs webhooks with).
• Infobip — a sender number, your API key, and your account base URL (the xxxxx.api.infobip.com host from your Infobip portal).

Connect with Telnyx

1. 1
   On the chatbot's Channels tab, add an SMS channel, choose Telnyx, and fill:

   Field	Value	Rules
   API key	Telnyx portal → API Keys	Required. Used as Bearer auth on sends
   Public key	Same page — the base64 Ed25519 key Telnyx signs webhooks with	Required. Must be the raw 32-byte key
   From number	Your SMS number in E.164 format, +1…	Required

2. 2
   Copy the webhook URL shown after connecting.
3. 3
   In the Telnyx portal, create a Messaging Profile, set its Inbound webhook URL to that webhook URL (method POST), and attach the profile to your number. Telnyx refuses to create the profile without whitelisted destinations (its anti-fraud list of countries you may send to — error 40331 if you skip it): include every country your customers text from, since AI replies go back to those numbers.
4. 4
   Sending beyond the US has two extra Telnyx gates worth knowing up front:

   • Some destinations only accept alphanumeric senders — set an alpha sender ID on the Messaging Profile (error 40306 is Telnyx asking for one).
   • Many countries (for example Pakistan, and much of MENA/APAC) additionally require that sender ID to be pre-registered with local carriers — error 40305 ("Alphanumeric sender ID … is not registered for the destination"). Registration goes through Telnyx support and takes weeks, so file it before launch, not at first send.

How Telnyx webhooks are verified

Inbound webhooks are JSON API-v2 events signed with Ed25519 over {telnyx-timestamp}|{raw body} — headers telnyx-signature-ed25519 (base64 signature) and telnyx-timestamp (Unix seconds). Two things follow:

• A timestamp older than 5 minutes is rejected (replay protection), so a replayed or long-delayed webhook never lands.
• The signature covers the body, not the URL — the webhook verifies on any host, which is why the same public key works across environments.

A failed verification returns 403 and flips the channel's health chip to Signature rejected — the clearest possible signal that Telnyx is calling you but the public key on the channel is wrong.

Inbound texts arrive as message.received events; delivery receipts arrive as message.finalized events on the same URL.

Connect with Infobip

Infobip has the widest global reach — strong MENA/APAC coverage — and registers senders for you.

1. 1
   Add the SMS channel, choose Infobip, and fill:

   Field	Value	Rules
   API key	Infobip portal → Developers → API Keys	Required. Used as App auth on sends
   Base URL	The xxxxx.api.infobip.com host — paste it as https://xxxxx.api.infobip.com	Required. Validated to match https://<subdomain>.api.infobip.com exactly — anything else is refused, at connect and again on every send
   Sender	Your SMS number	Required

2. 2
   Copy the webhook URL shown after connecting — it already carries a ?secret=… query param, shown once. Treat the whole URL as a credential and keep it private.
3. 3
   In the Infobip portal, set that full webhook URL (including ?secret=) as the number's inbound-message webhook and its delivery-report webhook — both point at the same channel URL.

How Infobip webhooks are verified

Infobip does not sign webhooks: the secret in the URL is what authenticates its calls, compared in constant time on every request. A call with a wrong or missing secret is rejected (403) and flips the channel's health chip to Signature rejected. There is no way to re-display the secret later — the connected-channels list masks it as ?secret=••• — so if you lose it, reconnect the channel.

A single Infobip POST can carry inbound messages and delivery reports together; both are processed.

Connect with the API

`POST /channels` takes the same credentials as either form. config.provider picks the transport, and omitting it fails 422 with "Pick a provider for this channel."

Telnyx — all four keys required:

{
  "type": "sms",
  "chatbotId": "3f2504e0-4f89-41d3-9a0c-0305e82c3301",
  "config": {
    "provider": "telnyx",
    "apiKey": "KEY…",
    "publicKey": "…",
    "fromNumber": "+15550001111"
  }
}

Infobip — all four keys required, and baseUrl must match https://<subdomain>.api.infobip.com exactly:

{
  "type": "sms",
  "chatbotId": "3f2504e0-4f89-41d3-9a0c-0305e82c3301",
  "config": {
    "provider": "infobip",
    "apiKey": "…",
    "baseUrl": "https://xxxxx.api.infobip.com",
    "fromNumber": "447860099299"
  }
}

Either way the response returns the channel's inboundSecret once. What it is for depends on the provider: on Infobip it is the ?secret= value the webhook URL needs, because Infobip does not sign its calls. On Telnyx the inbound webhook is authenticated by the Ed25519 signature instead, so the URL carries no secret. The same credentials connect Voice and WhatsApp — only type changes.

Verify it works

There is no in-app test button — verification is real traffic. Text the number: the message should appear in the Inbox tagged SMS, and the AI should text back. The channel's health chip narrates the result:

What happens to an inbound text

Understanding the ingest pipeline explains most behaviour you will observe:

1. 1
   Contact — the sender's phone number is matched to (or creates) a contact, so the thread is linked to a person from the first message.
2. 2
   Dedup — each provider message id is remembered; provider retries of the same webhook never create duplicate messages.
3. 3
   Threading — the text joins the sender's existing open SMS conversation on this chatbot, or starts a new one if the last one was closed. The same phone number talking to two different channels stays in two separate threads.
4. 4
   AI reply (if AI replies is on) — the reply is generated after the webhook is acknowledged, so provider timeouts never race the model.

Inbound MMS is supported: media URLs ride along with the message (up to 10 per message on Telnyx; one on Infobip), and a media-only text still arrives as [Customer sent an attachment] plus the link. Those links belong to the provider and can expire — download anything you need to keep.

AI replies and human handoff

SMS honours the channel's AI replies toggle (on by default):

• On — the AI answers new inbound texts with the same grounded pipeline as the widget, subject to your message quota, credit balance, and spend cap. A sender who asks for a person is escalated: the thread flips to needs_human, enters the inbox wait queue, and gets the fixed acknowledgement ("Got it — connecting you with a member of our team…").
• Off — every new inbound thread lands in the inbox already flagged needs_human, with alerts for opted-in agents. Nothing is auto-sent.

If an AI turn cannot complete — out of credits, over quota, a provider failure — the thread degrades to that same wait queue with that same acknowledgement. A failed turn is never left as silence. The AI also stays quiet on any thread a human has already claimed, and on closed threads.

One deliberate design choice worth knowing: the AI reply runs at most once per inbound text. There is no retry queue, because an SMS send has no idempotency key and a retried turn could double-text the customer. If a turn dies mid-flight, the thread degrades to the human queue instead.

Outbound replies

Replies — agent or AI — go out through the conversation's own channel:

• Telnyx — POST https://api.telnyx.com/v2/messages with your API key.
• Infobip — POST {baseUrl}/sms/3/messages with your API key.

Before sending, every reply is normalised to plain text: markdown links become label: url, headings and bold/italic markers are stripped, code fences unwrapped. No stray Markdown reaches a phone.

A reply always leaves from the conversation's own chatbot and channel — it can never be delivered from another bot's number. If the exact originating channel was deleted, the oldest active SMS channel on the same bot is used; if the channel is merely paused, replies to open threads still go out (pause blocks new inbound only).

Attachments cannot be sent on SMS — outbound is text-only, and agents see "Attachments aren't supported on this channel". Send a link instead.

Delivery receipts

Both providers report what happened to each send, on the same channel webhook, and the status is synced onto the reply's row in the console:

Statuses only move forward — a late or reordered receipt can never downgrade a message. A failed send stores the provider's reason on the message and offers a one-click Retry.

Keep replies short

SMS renders no formatting, and long messages are split by the carrier — the platform does not segment, count characters, or truncate; text is passed to the provider verbatim. For an SMS-heavy deployment, set the chatbot's max reply sentences so the model composes short answers in the first place — see Chatbot settings.

Duplicate numbers

One number and channel type map to a single inbound webhook, so a second channel on the same number would silently starve the first. If the number is already connected to another chatbot for the same type, the connect form shows a duplicate-number warning naming that bot. You can still proceed deliberately — for example when migrating a number between bots.

Settings and lifecycle

Credentials are stored encrypted at rest and decrypted only server-side per use. There is no pending/verifying state — a channel is live the moment it connects; the health chip is what tells you whether traffic is flowing.

Limits

• Inbound webhook: 120 requests per minute per channel/IP; beyond that the provider gets 429 Too many requests.
• Inbound body: 2 MiB cap (413 past that).
• Telnyx signatures: 5-minute replay window.
• Inbound media: up to 10 attachments per Telnyx message, 1 per Infobip message.
• Outbound: text only — no MMS.
• No STOP/opt-out keyword handling in the platform — unsubscribe keywords are handled (or not) at the provider/carrier level. If your use case requires opt-out compliance, configure it with your provider.

Troubleshooting

Where to go next

• WhatsApp via Telnyx or WhatsApp via Infobip — the same credentials, a WhatsApp sender instead of an SMS number.
• Voice — the same Telnyx or Infobip account, a different pipeline.
• Channels overview