@NeoCZ 

What are the configs? It would be helpful to see some pictures of your WAN VLAN and LAN VLAN config. 

From my past experience, it is not recommended to set up your WAN and LAN with the dup numbers(like IP, VLAN ID and etc.). 

  @John1234 

I just have default LAN, so only VLAN ID 1 is used in LAN. I need to set up WAN and WAN/LAN1 ports to us PPPoE connection with VLAN set on both ports to 848. If I set WAN to VLAN 848 and WAN/LAN1 to VLAN 849 it works, but I need both to use VLAN 848. Error message is "This VLAN already exists in one site."

  @NeoCZ 

OK, I see. Do you mean that both your WAN and WAN/LAN1 connection requires the VLAN and they have the same VLAN ID 848? Same ISP?

  @John1234 

Yes, that's right, both WANs need same VLAN ID. ISP is the same but bonding is not possible from his side, so I need 2 separate connections.

  @NeoCZ 

 Not sure about this. Is there any other router that supports dual wan with the same VLAN ID? From what you described, it seems ER605 does not support such a connection. So, at this time, I could only think you put up a router for WAN/LAN1. Should be ISP---Router PPPoE with VLAN ID----ER605(WAN/LAN1).

  @John1234 

Actually I have found one from DrayTek Vigor2960. But I would like to simplify my setup, not to add another device. I know I can use other router and put it between IPS and ER605, I just have hoped there is a way to do this only with ER605.

  @NeoCZ 

Got it. Yes. I know double-nat is annoying. Worth some consideration. @Hank21 

  @NeoCZ 

A workaround.

https://community.tp-link.com/en/business/forum/topic/274820

  @John1234 

Thanks for workaround but still, direct support would be better. Is there any way how to officially make feature request?

  @NeoCZ 

There is a request section. They browse regular forums like this section too. Think TP-LINK agent will record this. @Hank21