The internet service provider I deal with does not use VLAN ID. 

  @nazmiuyar 

Hi,

On a TP-Link router, if you don't require the VLAN ID, then you need to turn this feature off (i.e. untick the tick box).

  @woozle 

Hello, there is no box selection to turn off the internet vlan id. I solved the problem like this: I selected "bridge" in the connection configuration. It only connected when I entered the wan username and password. When we select the "private" option at the connection stage, it asks us to enter a number for the internet vlan id and cannot make the pppoe connection.

  @nazmiuyar 

Ok, it sounds like you were going through the Quick Setup, right?

If your ISP does not require VLAN ID, then you should not select any VLAN ISP Profile. Just leave it at "None", which is the default setting and means Internet VLAN ID is not used.