Hi  @BruBru ,

If your client devices have no Internet access when connected to the Range Extender's Wi-Fi, check the LED status on the extender and refer to the situations below to troubleshoot: 
Situation One: Signal/2.4G/5G lights are all off or signal light is red. 
    1). Ensure the extender is within the Wi-Fi range of the host router. Move it closer to the router. 
    2). Restart the router and the extender. 
    3). Hard reset the extender and reconfigure it. 
Situation Two: Signal/2.4G/5G lights are on: 
    1). Ensure the router's Wi-Fi is working properly. 
    2). Restart the router and the extender. 
    3). Upgrade the extender's firmware to the latest. 
    4). Turn off any Mac address filter or Access Control feature on the host router. Please contact the router support for detailed instructions. 
    5). Compare the IP address obtained from the router and the extender. If they are not in the same network segment, enable the DHCP server on the extender. Check this link for detailed guidance: 
What's the solution if my TP-Link range extender can't connect to my router properly?
 
Situation Three: Only one device/client cannot access the Internet
    1). Reboot the device and the extender. 
    2). Try connecting the device to a different Wi-Fi network to ensure it works. 
    3). Update the network adapter of the device.