How do I connect a Unifi Cloudgateway Fibre directly to my ONT?

Hi Community, 

I am trying to connect my Unifi Cloudgateway Fibre direct to KPN’s ONT using the following steps:

1.  I have used the ethernet cable provided by KPN to plugin to Port 5
2. During connection I selected the manual configuration option and entered the MAC address of my KPN box 12 router and waited for the system to update.
3. I then entered my pppoe details 
4. Set the vlan id to 6 
5. set the primary and secondary DNS server IPv4 and saved. 

After the above steps I am then taking to the internet speed page where I can see a connection, but then quickly after that the device looses connection to the internet and the data light on the ONT turns blue. 

Can someone please let me know where I am going wrong because I have been going at it for 2 days now and still unable to access the internet.

Thank you in advance.​​​​​​​