Hi there @RonL ,
Welcome to the Community.
My apologies, as customization of an opt out message with a toll-free number is not an option available at this time. With this setup, customization for unsubscribe keywords is restricted outside of Stop, Stopall, Unsubscribe, Cancel, End, or Quit. For the current time being, I would make sure your SMS opt-out language specifically references one of these terms so that users unsubscribe successfully. However, we are looking into adding more opt out messages for SMS, so keep an eye out for future updates.
Please take a look at your SMS settings (Account > Settings > SMS) and scrolled down to the Keyword Management section:
https://www.klaviyo.com/account#sms-settings
To note, customization of certain keywords are restricted, such as when a profile is unsubscribed, as well as resubscribed. I apologize for any inconvenience this may cause!
I'm happy to provide this article here on How to Add, Update, or Delete Custom Keywords if you would like further detail about this.
All the best,
Alex