Problem with Google VR Instant Preview

Hi,
I want to have an instant preview to skip the build process and test my VR app instantly on my android device. I imported Google VR SDK for Unity then I added a Google VR GvrInstantPreviewMain prefab to my VR app scene. After running the scene, an Instant Preview application was automatically installed on my android phone. But, when I am running my app in the Unity3D editor. It cannot connected to the Instant Preview app and does not show anything on my phone.

I have checked the Google VR SDK demos’. All works fine. It seems something is wrong with my app. Does anybody know how to solve it?

Thanks.

I have found the problem. My main camera did not have any Tag. For running the Google VR Instant Preview, it seems that the Main Camera must have a MainCamera Tag.