@DanielDT Try the setting Use the following IP address: 192.168.0.254 (like in my screenshot). Restart the router, the restart the RE and test. Don't forget to update the RE firmware as I posted...

@DanielDT When TL-WA850RE is wired to your main router it should be in configured in AP mode - details. Even in a range extender mode (connected wirelessly) it has LAN settings: By the way - there's...

@Hutki_Shira Deco mesh is not compatible with Easymesh or Onemesh - details. The configuration you're targeting is possible though - RE450 wired to Deco S7 should work in AP mode, but not in mesh.

@Anwesha_12 Have you try to configure the RE via web browser - details. Also make sure that your RE is with the latest FW release.

@DanielDT Can you post your TL-WA850RE LAN settings ?

@Dani111 What's your AX72 FW version. If it's not the latest one, update it and check if there's any improvement - here. How to update the FW of your router - details.