Fitriana, Selsabella, et al. “Analysis of Customer Relationship Management (CRM) System in Sales of Plus Hajj Product in PT. Fajrul Ikhsan Wisata (ESQ Tours Travel)”. ICHELSS: International Conference on Humanities, Education, Law, and Social Sciences, vol. 2, no. 1, Nov. 2022, pp. 953-61, https://journal.unj.ac.id/unj/index.php/hispisi/article/view/31004.