We're working on that now. We put aside all the financial stuff for a while so we could focus solely on getting chapter 4 done. Now that we're nearing completion of chapter 4, we can actually address the other stuff, including payment providers.
If you like, you can always head over to our Patreon (https://www.patreon.com/alterworlds) and support us there. Even the $1 options helps! We're glad you enjoy the game enough to want to support it, and we hope you'll like chapter 4.