Install is done through TestFlight (This is an Apple owned app which is used to install apps on phones prior to submitting to the store) The reason it’s done this way is that these types of apps are not allowed in the store.
Step 1: Press the ‘Test Flight’ button above to install TestFlight onto your phone
Step 2: Once TestFlight has been installed, come back here and click the “Download” button
Step 3: Follow the steps given to complete the install
If you need any help or run into issues, please contact us at firstname.lastname@example.org