No, we do not have access to the manufacturer's PK/KEK, so I created my own keys and certs. Theoretically, to debug this you can send me the GUID/Name and payload you are trying to write, I can check if I can write your variable with my tool and signing. Then I could look at your code and compare with mine and see why it does not work. If your code works on my devices, maybe the specific model you have has some issue? BTW, try the other vendors, like Lenovo and HP. I only cannot promise when I will be able to get to it with holidays approaching and many other things to do...