hello Terr,
if the "powerline" LED(The second light) is no longer lit, meaning the powerline connection is disconnected.
if that's your situation, i may suggest you try below:
way1: use the "pair" button to pair up the device,
so hold pair on small one(TL-PA211) for 3seconds, then hold TL-WPA281 for 1-2seconds, this action must be taken within 2mins.

way2: connect computer to TL-WPA281, and then load the management utility/powerline scan on your windows computer, login to the TL-WPA281 with
user name: admin
password: admin
after login to the magement utility, go to powerline, then station setting to add the DEVICE PASSWORD of the corresponding one(TL-PA211) into TL-WPA281,
so they can recognize each other, if they do recognize, it will show up as "online" after adding the device password.
hopefully, it works for you.