TP-Link TL-WA855RE User Manual page 15

"Connect successfully" will appear on this page, which means that
your client device has connected to the AP by WPS.
Method THREE: Enter the AP's PIN code on your client

device
Use this method if your client device requires the AP's PIN code.
Launch a web browser, log into http://tplinkrepeater.net, and then
go to Settings > Wireless > WPS page.
Enable the WPS function of the AP.
Enable the AP's PIN. The current PIN code of the AP is displayed
here, you can click Generate to get a new one.
On your client device, enter the AP's PIN code. When the AP's LED
is solid on, the client device has successfully connected to the AP.
Connect the Extender to the Internet