Hamdan, Hamdan, and Hapzi Ali. “The Effect of Loyalty Points, Tiered Membership, Gamification, and Free Shipping on Customer Retention: A Study of Loyalty Programs in Online Shopping Applications”. Greenation Education and Culture Review 1, no. 2 (September 1, 2025): 53–60. Accessed March 3, 2026. https://greenationpublisher.org/GECR/article/view/605.