Proximus and Scarlet decoders will only work with an external IP Address. If your TV Decoder is connected to your private router, behind the ISP’s router (b-box), you will need to move the switch connection to a VLAN. Here’s how this can be done with DD-WRT router firmware (Firmware: DD-WRT v3.0-r40189 giga (07/04/19).
connect to your private router;
go to setup and select Switch Config;
select the switch Port of the TV Decoder connection on the router (e.g. Port 3);
deselect the VLAN1 option (LAN);
select the VLAN2 option (same as WAN Port)
save the configuration and apply