If you want to make your output Stereo with a Mono input, please follow the steps below:
1.In the VST Connections > Input, Add a Mono Bus.
2.Then Add Stereo Audio track in the Project window. As an Input, select the Mono In, you just created.
This will create a Audio part, which will be mono. But the output will be stereo, and you should be able to apply the stereo effects.