A little convoluted but you only have to go through the ordeal once:

So here's how you can get a pretty decent app that'll work with Fapchan. It's Android only, sadly. But maybe we'll have better mobile support in the future.

The first thing you need to do is enable the installation of unsigned APKs. Google forces this on you because they don't want you to run applications from outside of their play store. In the case of Apple, they don't even give you the option to run unsigned software, and completely lock you into their ecosystem. This guide will show you how to enable the installation of unsigned APKs (Android Applications) https://yourbusiness.azcentral.com/install-unsigned-android-app-9807.html

After doing that, follow these instructions to learn how to install the app.

1) Install Dashchan ( https://github.com/Mishiranu/Dashchan-Extensions/raw/master/update/package/Dashchan.apk )
2) Install the Endchan extension (https://github.com/Mishiranu/Dashchan-Extensions/raw/master/update/package/DashchanEndchan.apk ) We do this because Endchan also uses LynxChan, so if we change the domain name in the settings we can use Fapchan or any other LynxChan based imageboard we want. Very useful.
3) Open Preferences
4) Open Forum
5) Set a default starting board, doesn't matter what it is.
6) Scroll down and set the domain name as fapchan.org.
7) Close the application and restart it.
8) After restarting the application, open preferences again.
9) Untick "Use catalog"
10) Browse the boards you want!

Edit: Add space to parenthesis because LynxChan link parser is silly.