Mobile App Onboarding

So I'm trying to understand the experience for a new user to a mobile app. My understanding is that first the user must be invited. this will send out an automated email from retool with a web link for them to setup their account after which they are taken to the web version of the mobile app. This is not an ideal setup. There appears to be no way to directly have the user setup their account on the mobile app itself. Alternatively there is no way for the user to setup their account on a web page that then directs or sends the user to download the mobile app. It just all seems so clunky and unuser-friendly. Also I can't get the auto-join domain to work. I select the option but I don't see any difference in the web login page. The documentation doesn't really explain how it is supposed to work for the end user. Can anyone who has had any experience with mobile app onboarding shed some light on best practices for creating a more seamless onboarding experience?