GRANTA app gyroscope function

Having used the GRANTA English literature application for many years now without being able to read the content horizontally on my iPad Air 2 i sent a request to GRANTA, why i can‘t achieve that. At the end i was told to ask APPLE, as their technical team wasn‘t able to provide an answer. I am only able to read the content of GRANTA books by holding my iPad in a vertical position, the gyroscopic function won’t work on this particular application. Does anyone within this community know an answer? Thank you! Peter