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I've innumerable smart devices from the likes of Meross and Kasa and although most of them are also 2.4GHz only, they've all readily connected to my home Mesh network, without having to switch off 5GHz - both 5GHz and 2.4GHz networks share the same ID; but not the Tenda SP9. For a start, the app (Tenda Beli) makes you manually switch between your network and the plug's 'Wifi', but even after switching the 5GHz network off, I was unable to connect the plug to the remaining 2.4GHz network. I've recently updated the smart phone to Android 11, so whether this was a factor I don't know.