I think you can change your membership level i did this one time afew months ago. Do you have to log in to driver4vr when you start steamv? That was when the membership level was needed so the trail version wouldnt stop the drivers after 10mins
I found some people with the same problem. But unfortunately I am not Greg but the best way to be in contact with him is via his facebook group.
Another method of contacting him is to hope for greg to see this thread.