u know how to keep ppl interested in your book? post frequently. it keeps your book in peoples newsfeeds  (which increases visibility) and the story stays fresh in peoples minds.

if you wait a month or even a couple weeks to update, you have people shrugging and going "wait what's happening again???" and then. people just stop reading

cant write that fast? make a queue. write a whole bunch of chapters beforehand and post them weekly, or even biweekly. keep yourself on a schedule. post often!