For pairing the Tuya Zigbee 3.0 devices (Melery, Loratap, etc.) to C8 hubs, use the Double Luck Voodoo. I suppose it won't hurt to try the same procedure with the Smarthings Multipurpose contact sensor as well.
Have tried the method, but no luck on either the melery and smartthings sensor. Couldn't test the loratap just then. I'll test an in wall switch tomorrow and see how it goes.
But for now, back to square 1 with the current devices
So i tried a Sonoff SNZB-02P temp/ humidity sensor - Did not pair.
Performed a soft reset on the hub , was able to pair the Melery GPO and sonoff sensor
Cos i paired the GPO using a fly lead near the hub, i turned off the power circuit installed the GPO in its location and switched power on - The hub booted into new hub mode and i lost the 2 devices - Now they wont pair again
Tried to pair a Moes zigbee switch module - No luck
Completely at a loss now as to why zigbee does not pair