Transactional SMS: what counts, the consent it needs, and templates that fit one message

A transactional SMS is a text a person needs because of something they did: a sign-in code, an order update, an appointment reminder, a password reset. A marketing text is anything that promotes. The difference decides the consent you need, the hours you may send in, and whether the text must end with “Reply STOP to opt out”.

Transactional texts still need the person to have given you their number for that purpose, and they stop when the person texts STOP. Keep each one short enough to fit in a single message: 160 plain characters, or 70 once a single emoji or curly quote creeps in.

The test is the reason the text exists. If the person would expect it because of something they just did, or something they arranged, it is transactional. If it is there to sell, it is marketing, even when it rides on a transaction. A shipping update is transactional. The same update with “10% off your next order” at the end is promotional, and the wireless industry treats it that way: CTIA's Messaging Principles say that adding a call to action such as a coupon code to an informational text may put the message in the promotional category.

In Rasket the kind is a field: category on a send, transactional by default. Calling a marketing text transactional to get past the rules is something carriers look for, and so do we: your number's registration already says how you will text, and a mismatch is a reason to be filtered.

Less than a marketing text, but not none. Under the FCC's rules, a text that includes an advertisement or is telemarketing, sent with automated equipment, needs the person's prior express written consent: a signed agreement, which can be a checkbox and an electronic signature, that clearly authorises the seller to text them ads at that number. A transactional text sent the same way needs the person's prior express consent, which in practice means they gave you the number for this purpose: at checkout to hear about the delivery, or in their account settings for sign-in codes.

CTIA's guidelines draw the same line in their own words. A conversational text answers one the person sent. An informational text, such as an appointment reminder, a welcome text or an alert, follows from the person giving their number and asking to be contacted, and they should agree to texts for that specific purpose when they give it. A promotional text needs written agreement first.

Canada's anti-spam law takes a different route to a similar place. Section 6 requires consent for a commercial electronic message, and lifts that requirement for one that solely confirms or completes a transaction, or gives warranty, recall or safety information. The rest of section 6 still applies to it: the message must identify the sender, say how to contact them, and offer a way to unsubscribe.

These are written for a brand called Acme, filled in with sample values. Each count is for the whole text as sent, which is how texts are billed: Rasket puts Acme: in front of every text that does not already start with it, and adds “Reply STOP to opt out” on a new line to the first transactional text a phone gets from you in any 30 days. The last column is that first text.

Acme: Your order #1042 has shipped. Track it: acme.co/t/1042
Reply STOP to opt out

Two of the rows are the same text with one character changed. The password reset with a straight apostrophe is one message; with a curly one, which phones and word processors type for you, the whole text switches to UCS-2 and needs two. An emoji does the same. Use straight quotes in your templates, and leave the emoji out of anything sent at volume.

A message is up to 160 characters (70 if it has an emoji or another special character). A longer text is sent and billed as several messages.

• GSM-7 is the phone networks' own 7-bit alphabet: letters, digits and common punctuation. A text that uses only it fits 160 characters in one message. A few characters, such as € [ ] { } ~ ^ |, are in its extension table and count as two.
• UCS-2 is used as soon as one character is outside GSM-7: an emoji, a curly quote, most accented letters outside the basic set, any non-Latin script. One message then holds 70 units, and an emoji counts as two.
• Longer texts are split into parts, and each part loses a few characters to the header that joins them on the phone: 153 GSM-7 characters or 67 UCS-2 units a part. Rasket sends at most 10 parts and refuses longer text.

Each part is a message you pay for: at $0.015 a message, a three-part text costs three times a one-part one. No character is quietly swapped for a lookalike to save a message, so what you count is what is sent. To count a text before you send it, call POST /sms/estimate, which returns the encoding, the characters, the messages and a warning such as special_characters.

Marketing texts in Rasket go out between 8 am and 9 pm in the person's own time zone, or the shorter hours some states set, the same window the FCC sets for telephone solicitations in the US. A marketing text due outside it waits for the next morning; nothing is dropped. A phone also gets at most one marketing text from you in any 16 hours, however it was sent.

Transactional texts skip both rules. A sign-in code at 2 am is still wanted, because the person asked for it a second ago, and a delivery update does not use up the one marketing text a phone may get in 16 hours. That is the practical reason to get the category right: a reminder sent as marketing would wait for the morning, and a promotion sent as transactional would break the rules that protect your number.

One call to POST /sms. Set category to transactional (it is the default, but saying so makes the intent visible in your code), and make the Idempotency-Key from the event, such as the order and what happened to it, so a retry within 24 hours returns the first answer instead of texting twice.

curl -X POST "https://api.rasket.com/sms" \
  -H "Authorization: Bearer $RASKET_API_KEY" \
  -H "User-Agent: acme-billing/1.0" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: order-1042-shipped" \
  -d '{
  "to": "+14155550123",
  "text": "Your order #1042 has shipped.",
  "category": "transactional",
  "tags": {
    "order": "1042"
  }
}'

const response = await fetch("https://api.rasket.com/sms", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.RASKET_API_KEY}`,
    "User-Agent": "acme-billing/1.0",
    "Content-Type": "application/json",
    "Idempotency-Key": "order-1042-shipped",
  },
  body: JSON.stringify({
    to: "+14155550123",
    text: "Your order #1042 has shipped.",
    category: "transactional",
    tags: {
      order: "1042"
    }
  }),
});

const { id } = await response.json();

The answer says how many messages the text was and what it cost, and webhooks follow as it is sent and delivered. The SMS API guide walks through the whole first send, from giving a key SMS access to the delivery webhook.

When the text belongs to a flow, such as a shipping update after an order event, add a Send SMS step to an automation instead of calling the API yourself. The step is send_sms, and its category is marketing unless you set transactional, so set it:

{
  "id": "text_shipped",
  "type": "send_sms",
  "config": {
    "text": "Your order {{{event.order_number}}} has shipped. Track it: {{{event.tracking_url}}}",
    "category": "transactional"
  }
}

• text takes the same merge fields as an email in the flow, including the event's own data.
• A contact with no phone, or who texted STOP, skips the step, and the run carries on with its next one; the run's history says why.
• from is optional; your default number for the contact's country is used.

Texts in automations has the full step.

Transactional texts go through the same API key, contacts and webhooks as your email, to phones in the United States and Canada. Every text says what it cost, a failed one is never charged, and STOP, HELP and the opt-out list are handled for you. Until your own number is approved, which usually takes 1 to 5 business days, you can send these templates to your own verified phones from Rasket's shared test number and see exactly how they arrive.

The SMS page has what is included, and Consent and STOP has the rules for the texts that are not transactional.