INSTALL and RUN a AMD Graphic Card on a VMu (Centos 6.9) run on XenServer 7.4

Just start using XenServer. Doing some experiment for my company. Installed XenServer 7.4 on a Box and created a Centos 6.9 VMU. Using XenCenter. Got to the point when I can run the virtual operating system but when i try to use the AMD graphic card with the command: xe vgpu-create vm-uuid=xxx-xxx-xxx-xxx gpu-group-uuid=xxx-xxx-xxx-xxx I receive the following error message: The use of this feature is restricted. I have also used the graphic interface using a licensed Xen-Server to enable the AMD card using the Tools->Install Update ([login to view URL]) to enable the Graphic card I cannot complete the process as i receive the error message: The attempt to create a VDI failed Do you understand where the problem is? If yes, I would like to share my screen via hangout and you can see if you can help and hopefully guide me to the solution.