@Sky_Blue 

What is the led status of the TL-WA850RE? 

Please connect your computer to the TL-WA850RE by wired cable directly to verify whether you can access internet. 

Try to disable and re-enable wifi function on your device and reconnect to the extender's wifi. 

Any updates, please let us know. 

Best regards. 

@Sky_Blue 

Thanks for your reply, the extender should be working fine cause you can get internet from it directly. 

For the wireless password issue, try to forget the network and reconnect to  it; below is the instruction (we take windows 10 as example).

https://www.tp-link.com/support/faq/918/

Still the same, you can hard reset the extender and reconfigure it. 

Note: Please give it a different network name.

May it help.