EnderDragon doesnt spawn

 

When i want to spawn the enderdragon its gives me back the Ender Crystals and doesn't do anything.

It happend in the end, in overworld and nether.

Its a free explosion because it gives me the ender crystal always, but i want to go to a end city and i cant do it if i dont spawn the dragon.

I was thinking to resolve this but the only thing that i think i can do is restart the end, but i have a lot of things there.

Sorry for the waste of time, i wish we can get a solution. Thanks