Imperial passport of Kublai Khan “I am the emissary of the Khan. If you defy me, you die.” (This is one of two known passports).
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A paiza or paizi or gerege (Middle Mongolian: Гэрэгэ, Mongolian: Пайз, Persian: پایزه pāiza, Chinese: 牌子 páizi) was a tablet carried by Mongol officials and envoys to signify certain privileges and authority. They enabled Mongol nobles and officials to demand goods and services from civilian populations.
To be fair, the Khan wanted to be his friend and he murdered his diplomats (who were likely members of the Khan's family) and dishonoured the survivors. I'd be a bit upset too.
Not, you know, enough to murder a city (wth Khan?!) but I'd definitely want the Shah's head on a pike, while he's still alive.