I've been running a Patreon site for my comics for a little over a year now, using it as a digital subscription service.
It gets some interest, but I could be promoting it a lot more, I think.
Patreon sets up a relationship between creator and consumer, in which someone pledges an amount paid upon delivery of content - if I don't put a book up, there is no charge!
I've got it set to a minimum $1 pledge amount (but you can pledge more if you want!)
Hope you'll consider checking it out, perhaps backing it, or sharing it with others.