Ask HN: Whitelabel "Paid Forum/Chat Mobile App”-in-a-Box

Hey HN gang, freelance mobile dev here - A potential client is asking for a "company-branded forum & chatroom"-as-an-app, where different sections of the forum/chatrooms have membership-access paywall, all with a super simple UI. Customers should be able to download the app in the Apple App store, and then pay/sign up for various sections of the community (e.g. they might need to be certified before joining). After some searching the web, I'm feeling a bit stumped. I'm hoping to find a (paid or open source) out-of-the-box, good UI, ready-to-go, "upload your logo / & customize colors & publish" type service (think: Shopify). To anyone with expertise in this area, can you suggest any solutions to look into? I'd love to get my potential client a response back ASAP with a couple reasonable options / level-of-effort estimates. Thank you for any info you can provide! -J * Full transparency, this is year #1 for me of iOS mobile app development, so with my current skill level, I'm hoping to cobble together existing solutions rather than build from scratch. Yak-shaving and all that :)