@Gerbil Follow this guide to troubleshoot the error. Don't use the PowerShell script for VLAN ID, you're doing it right so far.

@liquidguru You're targeting Primary DNS field.

@liquidguru Go through this thread to find your answer.

@Fahl I misunderstood your description - you're referring to C2300 hairpinning. TBH I am not sure if it supports it - the only thread I've found on that matter is here.

@Barcafan You can't have mesh network between two routers - Q10/A10. Your R600VPN is a SafeStream Gateway, part of the Omada-SDN solution for business. You can buy a JetStream switch like TL-SG2008...

A similar fix here related to QNAS TS-251. As @FreeLink posted lets hope that's informative for TP-Link Tech Support troubleshooting purposes.