How do you make a fictional religion for a fantasy story?
So I happen to be new to writing and I’ve been working on a fantasy story, but I kinda ran into a problem on how I can create a fictional religion. I’ve already been taking inspiration from real life religions like Catholicism and orthodoxy since there the two religions that interest me the most and because I happen to be somewhat educated on thomist theology.(no I’m not a scholar I just like learning theology)
Im hoping to get advice on how I can do it and what it takes to make a religion in a fantasy feel somewhat real and what should I avoid while I create the religion?
Thanks in advance to anyone who gives me advice I very much appreciate it