Double opt-in is mandatory in Canada. These SMS confirmation messages must be on in order to add subscribers.
SMS double opt-in for Canada works like this:
The customer agrees to subscribe and then receives an SMS message asking for confirmation.
Then, in order to be treated as a subscriber, they must reply with one of these words/texts to confirm their subscription: “Yes”, “Y”, “Go”, “Okay”, “OK”, “O.K.”, “Sure”, “Yep”, “Yeah”.