PDF documents cannot be viewed on mobile devices

On this website—https://www.pfri.uniri.hr/web/hr/jugolinija.php—PDF documents open correctly using an Adobe API key on both mobile devices and desktop computers. However, on this website—https://www.pfri.uniri.hr/web/hr/dzgl_rijeka-test.php—which uses the exact same API key, the PDF documents are visible only on desktop computers; on mobile devices, I receive an error stating that the domain `pfri.uniri.hr` is not registered. What is happening, and how can this be resolved?