Hello! By setting the glass mat, there is no problem with it. To ensure you can download any other V-Ray material glass , which certainly works, and apply it in your scene. If he just is not transparent, then it is not in the material.
Check the roll-Ray of Global the V switches , whether or not there is a check mark in front of Reflection / refraction. It is responsible for the global off reflections / transparency (refraction) in the scene.
In addition, similar to the way you opened the window «VRay object properties», open the window «Object Properties», clicking the right mouse button on any part of the viewport and choosing the appropriate option. There's a section Rendering Control, check whether or not a check mark Visible to Reflection / refraction. Or simply create a new object of a simple glass Box and apply a new mate😉