Before you start working with devices, ensure you have an available device slot in your account — you may find it on the "Manage devices" page. Once you sign in to Setapp on Mac, this computer is displayed. An "Available device" slot shows that you can use another Mac, iPhone, or iPad with Setapp.
Connect iPhone or iPad
You don't need to sign in to Setapp on your iOS device or link it to Setapp manually — actually, there's no way to do that. iPhones and iPads connect automatically when you install and activate an iOS app using Setapp on your Mac.