@Akual

Hello,

What is the model number of your range extender?

If the extender has no internet access after the configuration, please check the RE light or signal Led on the extender.

Then please refer to this article to do the troubleshooting: https://www.tp-link.com/en/support/faq/2234/

Note: When checking the router's wifi password, please also confirm that the authentication type and encryption type is Auto on the main router.

If still no Internet， please help us confirm some information:

1. What are the Led Staus on RE after setup? Please let us know the troubleshooting steps you have tried in details, thank you!

2. The model number of the main router? Do you try to extend 2.4G or 5G wifi from the router? 

3. After configuration, please log in to RE's web page and send us a photo of the Status page, wait for 3-5 mins, save the system log and send us the log file.(System tools-> system log)

4.  The firmware and hardware version of RE: 
https://www.tp-link.com/support/faq/315/

4. May I know how long do you have this RE and when did the issue start? 

May it help and have a nice day!