Arvind Kejriwal's Singapore visit: Why do CMs need permission to travel?

The centre has denied permission to Kejriwal to visit Singapore. He is invited to Singapore’s World Cities Summit which is happening from July 31- August 3. This isn’t the first time Kejriwal faced hiccups in travelling abroad. In October 2019, Kejriwal was not allowed to go to Denmark. Why do CMs need permission from the Centre and what's the process? Watch to know more.