When was the Bulgarian state first recognized by the Byzantine Empire?

The Bulgarian state was first officially recognized by the Byzantine Empire in 681 CE.123

Following the migration of the Bulgars led by Asparukh across the Danube, the Byzantine emperor Constantine IV attempted to expel them from the region between the Balkan Mountains and the Danube. After the Byzantine forces were defeated, the empire signed a treaty recognizing Bulgar control over the territory, an event that marks the official founding of the first Bulgarian empire and the beginning of the Bulgarian state.23