This issue only needs to be tested in 1 device. In Moodle web as admin, go to "Site administration > Users > Policy settings".  Set sitepolicyhandler to "Default (core)" and enter any URL in "Site policy URL". In the app, login with a user that hasn't accepted the site policy. Check that the app displays a page to accept the site policy. Check that the button says "I understand and agree to the mandatory site policies". Logout and go to create a new account in the site. Check that you see a link to the site policy and the button says "I understand and agree to the mandatory site policies".