Text Opt-In Flows

There are two primary ways to get opt in for texting: single-opt-in and double-opt-in. Each method will ensure that the person subscribing to your text messaging is compliantly added to your lists.


In this method, you advertise your textable phone number and keyword on a website, email, or other collateral. The keyword (shown as TSO below) is completely customizable / configurable.

To join our text list, text TSO to 1-888-555-1212. Text message rates apply. Reply STOP to opt out.

Note that SMS is a valid html href tag and can be embedded in the webpage or email. In these cases, if the contact clicks the link from a mobile device, the phone will open to the given phone number:


<a href="sms://+18006050280">Join the TSO Text List</a>

Example with body

Clicking this link would automatically open SMS on the phone to the given phone number with the text TSO pre-instantiated in the message text — all the contact needs to do is hit Send.

<a href="sms://+18006050280?&body=TSO">Join the TSO Text List</a>

Data Tie-Back

In some cases, it may be useful to be able to associate a contact that has gone through this single-opt-in process to your underlying contact data. Opt in flows can be quickly deployed to gather appropriate information to enable this — for instance, on first text, you can ask for their email address — and if provided, an API call can be made back to the system of record associating the phone number with the associated email.


In double opt in, you surface a form on a web page and ask the contact to enter their phone number. On submission, a text message is sent to the given number:

Thank you for your interest in joining the TSO text list. To confirm you wish to be added, reply TSO. Text message rates apply. Reply STOP to opt out.

If the contact replies TSO, you now are deemed to have express written permission to text with the contact with automated text messages.

Prompt.io has pre-built forms for double-opt in. Or, if you have your own developers you can surface an opt-in form yourself and call our API to kick off the double-opt-in flow.

An example of a double-opt-in flow can be seen at Prompt.io/contact-us.

Opt-In Automation

On successful opt-in, Prompt.io can be configured to interface with third party systems by either calling an API endpoint of your choice or posting to a webhook.

Handling Opt Outs

Prompt.io automatically handles all carrier keyword opt-outs. If the contact replies STOP, they will be removed from the list and blocked from further texting. Further automation can also be triggered — for instance, on opt-out, Prompt.io can be configured to call an external API endpoint or post to the webhook of your choice.

List Management

Opted-in contacts are fully managed via Prompt.io contact lists. Lists can be segmented by geolocation (if provided), tags (VIP, Ticketed), or data (State == Tennessee).


Compliant broadcasts to opted-in subscribers are fully managed by Prompt.io. Broadcast messages can be easily field-merged:

Hello, {first}! We have a new tour date in {state} on December 13! Click to purchase tickets: {link}

MMS — sending video, photos

MMS is fully supported by the platform via broadcast messaging. MMS supports a wide variety of file formats. Video is limited to 500kb by the carriers (ATT, Tmobile, etc) which if compressed properly results in 15-20 second video delivery.