I'm traveling a long road - self inflicted in some sense. I have a Loratap Relay wired to a 2.0 liftmaster remote control.
My unit either is broken or flawed by I/O (inputting operator) and I'm not using an available driver due to being directly wired to a remote control AND the free, built in sensor not working.
I installed the App Virtual Garage Door Controller.
After hoping someone else would do it, I ended up writing my own driver to control the device and all works perfectly!
Then I advertise it to Alexa - and slap! no... no worky.
I advertise the Relay and it DOES show up (recall I'm NOT using the relay software that does this - it was just to see what might be different).
Between the two devices, the Capability of Actuator is non-existent on the Virtual Controller. But the Capability GarageDoorControl is there. Would that me the reason Alexa is barfing on this? Here's my screen - note the greyed out "unsupported".
I use the Zooz garage door app and the virtual garage door has these capabilities:
capability "Actuator"
capability "Sensor"
capability "Contact Sensor"
capability "Door Control"
capability "Garage Door Control"
Works fine sharing to Alexa for me.
What driver is your virtual door device using? If its a custom driver you can just add capabilities to it yourself to see if that fixes it.
If you want a device driver to allow a device to do something, they basically need the actuator capability:
is that capability with "Garage Door Control" or capability "GarageDoorControl"?
I'll fart with choices and see if I can dislodge.
thanx
Both will work, HE ignores the spaces within the string when parsing the capability name.
You will need to implement the open() and close() methods - call the on() and off() functions there and send a 'door' event 
door- ENUM ["unknown", "closed", "open", "closing", "opening"]
