In the current version the abandoned-cart sequence sends to every abandoned cart owner who has a phone number; it does not check the customer's Receive SMS? toggle or the marketing groups' opt-out logic. If you are in the US or Canada, opt-out replies (STOP) are handled by the carrier-level messaging service, which blocks further delivery to numbers that have opted out. If you need strict opt-in handling for this reminder, keep the sequence off or contact Sprwt support.