Why can't I buy books and adventures in the mobile app anymore?
From version 10.0.0 of the Quest Portal app for iOS and Android, the Marketplace is only available on the web. The app no longer has a Marketplace tab, paid adventures no longer appear when you create a campaign, and if you try to buy a book in the app you'll see "Marketplace is only available on the web".
Nothing you own goes away. Every book and adventure you bought or claimed, in the app or on the web, is still in your Library in the app, and owned adventures still appear when you create a campaign.
To buy something new: open https://www.questportal.com/marketplace in your browser, sign in, and buy or claim it there. It appears in the app's Library straight away.
Your plan is separate. You can still start a trial or manage your Core or Pro plan in the app, under Settings > Subscriptions > Membership.
If you're on an older version of the app, the Marketplace tab is still there until you update.
See Marketplace and Mobile App Features.