LOGIN FAILED[0x0021006E]

I cannot log into the game today even I have tried numerous times
My progress is linked to my Facebook so I always choose Facebook in the 'Login to start' menu

Then it will lead me to the Facebook page asking me whether to continue
Every day it had been working fine

But today after pressing continue in the Facebook page it goes back to the FC Mobile app saying 'LOGIN FAILED[0x0021006E]