This function can be used to opt customers in or out of the loyalty program. An opted in customer / loyalty member can earn/redeem points and get into tiers. An opted out customer will lose point balance and tier status. You need to pass the shouldOptIn with true, to opt a customer in, or false - to opt them out. If you wish to also award a customer with the create account campaign upon opting in, you should pass rewardOnOptIn:true as one of the opts.