This pairing failed error started about a year ago. 4 c121 were installed without issue. When a 5th c121 camera was purchased to expand the system about a month later is when the pairing failed error started. There were no known changes that had happened.

No one could solve the problem including TP-Link Tapo support. Support said the camera was defective. Replacing the camera did not resolve the issue though.

Nearly a year later, the camera was replaced (with a c121) again because support said the second camera was defective too. Again the problem was not resolved.

I am now going to share the solution I finally found after a year of google searches and finally piecing many posts together the past two days with trial and error to get to a solution. I am sharing everything I tried because your situation is likely somewhat different and what did not work for me might work for you or give you an idea. At the end I'll summarize the problems I identified as well as the solution that worked for me.

The google search I did yesterday that led me solving this was the meaning of the superscript 5 with the wifi signal icon on the Android phone I had the Tapo app installed on. It meant I was connected to a 5 GHz signal. Then I installed the free app NetSpot. That's where I could see the two identical SSIDs with one being 2.4 and the other 5 GHz. I had just thought the equipment I was connecting to must have been so old there was only 2.4, and that is why there was no SSID with "5 GHz" as part of it's name. I did not set up the access point as a router nor can I control its set up.

These are all the ways I tried to connect to the 2.4 signal that failed:

*Using phone software to filter and select 2.4 signal (the 2.4 signal was not even visible in the Android OS).

* Walked outside till I lost the 5 signal then I turned off auto reconnect.

* Walked outside till I lost the 5 signal then I turned off auto reconnect and randomize MAC address.

* Searched for an existing app to solve the problem e.g. wifi manager.

* Created a wifi hotspot (to connect the Android phone to for set up using Windows 11 Pro, no VPN and with the 5 GHz set to not auto reconnect. No matter what SSID and password I used or if I scanned the QR code to connect, I could not see or connect to the wifi hotspot only the 5 GHz signal.)

* Block the 5 GHz signal by going the furthest distance from router in the house or placing the phone in the washer with metal drum, oven, freezer, refrigerator, and under metal frame of recliner.

I found two problems. The first problem I identified is the Tapo app cannot find and use a 2.4 GHz band wifi signal on it's own. You must be able to select it and be using it. The Tapo app will use a 5 GHz band wifi signal but not for bluetooth pairing. It would be helpful if the Tapo app error said "Pairing failed - no 2.4 GHz wifi connection (required for pairing)." The second problem is the wifi signal I was connecting to had the same SSID for the 2.4 and 5 GHz signals, so I could not connect to the 2.4 signal while having the camera plugged into power. Note: Extension cord(s) should work if long enough as well as using existing car outlet (or creating an outlet using cigarette adapter).

The solution that worked for me was to use a power station (to power the camera) and go the distance outside till I was sure the 5 GHz signal was unreachable but the 2.4 GHz signal was connected and strong enough. Then go thru the process of adding the camera in the Tapo app after factory resetting the camera. Note: The Tapo app works on a 5 GHz signal after adding or set up cameras.