I have tried adding them through the Wemo app directly. One way will pop me over to HomeKit, which doesn’t allow it to join saying it’s “uncertified”. The other method in the app directs you to connect to the plug’s wifi. However, because iOS’s wifi settings sees this as an accessory it seems to always direct me back to HomeKit. I did have a moment where it connected to the wifi and the Wemo app allowed a manual setup, but it seemed like my iPhone eventually figured out it didn’t have an Internet connection and swapped back over.