Still unable to complete Regular Customer goal for Self Care aspiration

Did you take into account Crin's advice that there is a cooldown?

Once your sim offers a spa service, the customer gets an 18 hour cooldown buff that prevents them from making any further progress. Have you tried picking one customer, giving them a spa treatment, then 24 hours later you invite that same sim over and give them another treatment, and so on for 10 days?