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SMS is far more regulated than WhatsApp. Two things are mandatory: honouring opt-outs and registering your traffic before you send.

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Keywords

Lumina recognises three keyword groups before the message reaches the model. They aren’t configurable.
The keywords are English only. There’s no Spanish list: a customer texting “BAJA” or “PARAR” does not trigger the automatic opt-out.In that case it depends on your prompt catching it. Add an explicit rule, for example: “If the customer asks to stop receiving messages in any language, confirm it and perform the opt-out.”

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Matching is exact

The keyword has to be the entire message, not part of it. "Please stop texting me" does not trigger it.
That’s deliberate: if containing the word were enough, a message like “stop by the shop at 5” would silently mute the customer, with no way for them to notice or undo it.Natural language is the AI’s job — it can perform the opt-out when it detects the intent.

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Opt-out is per contact

Not per conversation: once opted out, that contact stops receiving messages on this channel, including future conversations. Releasing it is done manually from settings. Opt-out confirmations are still sent even when the contact is already suppressed — that’s what regulation requires.

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A2P 10DLC registration

In the United States, all business-to-person traffic on local numbers must be registered. It isn’t handled inside Dialtu: it’s a process with the carrier.
Start this before anything else. Approval takes days to weeks. It’s the critical path of any SMS project.
Things worth knowing before you submit:
This is the most common rejection reason. The legal name and number must match what the tax authority holds, character for character — a trading name won’t do.
Register it as conversational / customer care, not as marketing.
Misregistering the use case is grounds for suspension.
If you leave the carrier’s automatic opt-out handling switched on, the customer receives two confirmations: the carrier’s and Dialtu’s.
Once the carrier records the opt-out, sends fail at the network level even if Dialtu still shows the contact as active. To receive messages again, the customer has to text START to the carrier, not just to you.

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Good practice

Identify yourself in the first message. Who you are and why you’re writing.
Mention how to opt out in the first message of any conversation you start.
Respect the hours. Use time-based routing so you’re not texting at 3am.
Be brief. Every segment is billed, and long messages get split.

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Back to the start

Introduction to SMS agents

The full path through this section.