Problem when join to conference room

Olá, this is my first topic!

I just created the conference room, without User and Admin PIN.
I used 300 to conference number and “Main conference” to conference name and keeped the others options as default.
Then, when I call to 300 number, I receive the welcome mesage “You are the first person to join this conference”, but when someone else connect, receives the same mesage and we can’t talk to each other.

Do I have to make a special configuration?