Do you really have to have an API call at the app launch to force users to the newest build in TestFlight or is there something in App Store Connect that will NOT allow users to use an older app build?

We have our app in TestFlight. To have new users signup requires two steps (not user friendly). The user clicks our link or scans are QR code. They get the page to show they have to download TestFlight and then install our app. Once TestFlight is downloaded and the user opens it, there is no app visible. The user has to click the link or scan the QR code again for it to show up in TestFlight. Has anyone been able to resolve this issue? Or is this just the user experience?