The SMS platform automatically unsubscribes all Opt-Out requests except for accounts on the Basic plan.
To ensure the unsubscribes happen automatically, use 'Reply STOP to OptOut' or in your marketing messages. When a recipient responds with a STOP, they are immediately unsubscribed and made 'Inactive' in your account and will not get any messages hereinafter unless a user changes their status.
Knowing that every Opt-Out request is managed correctly ensures that you will always respect your customers wishes and also be legally compliant.