Before 1.11, this command would summon a firework entity.
/summon FireworksRocketEntity ~ ~ ~ {LifeTime:20,FireworksItem:{id:fireworks,Count:1,tag:{Fireworks:{Explosions:[{Type:0,Flicker:0,Trail:0,Colors:[16777215],FadeColors:[16777215]}]}}}}
Since 1.11, it generates the "Unable to summon object" error in the command block. Is there a new way to summon firework entities?
Entity ids changed, use the tab auto-complete function to see a list if valid ids.