Why were Byzantine rulers unhappy with Charlemagne and coronation as Holy Roman Emperor?

Byzantine rulers were unhappy with Charlemagne's coronation as Holy Roman Emperor in 800 AD because they viewed it as a challenge to their authority and legitimacy. The title implied a revival of the Western Roman Empire, which they considered a direct affront to their own claim as the heirs of Rome. Additionally, the crowning by Pope Leo III signified a shift in power dynamics, undermining the Byzantine emperor's position as the leading Christian ruler. This event heightened tensions between the Eastern and Western Christian worlds.