First of all, please make sure your Yocan Evolve-C device is fully charged.
If your vape pen low battery, it can't produce any cloud.
Than, check all connections, and you can use a q-tip to clean all contact points.
5 taps to turn it on, and hold the fire button when you inhale.
If still can't work, please contact Yocan after-sale team for help.