Did at reset the light flash? Because that shows a reset.
Switching on/off need to be very fast
i do always 7 times on/off with the switch for a reset. You need a fysical switch of the power every time switching)
How many Zigbee-devices are already paired with your Homey? If you have a lot of end-devices (battery-powered, like sensors) it’s easy to reach Homey’s “directly-connected-devices” limit of about 20.
I have just added 16 Tradfri GU10’s for our just renovated house. About 10 out of 16 worked perfectly, and some required to be resetted twice. All of them finally worked without problem.
If the unit does not want to reset to factory settings, unplug it. Wait for a couple of seconds, and reset it again by flipping the switch 6 times. Make sure it’s not 5 or 7 times, it won’t work.
Programming was done at approx 2 meter distance from Homey.