Try to follow the steps in this link:
If you have issue with the most current distro iso, then try this iso image should work
https://downloads.freepbxdistro.org/ISO/SNG7-FPBX-64bit-1805-2.iso
I tested this iso on a local VM that is VHD. (VMDK
may work as well https://cloud.google.com/compute/docs/images/importing-virtual-disks ) wit fixed size.
Make sure you create a service account and download the JSON file Migrate to Virtual Machines documentation | Google Cloud
Here is some more guide https://www.youtube.com/watch?time_continue=39&v=R9JDCRCro-s
If you manage to have the VM instance up and running I recommend making Snapshot. I had issue updating the FreePBX system from the web interface. I recommend logging into your system via SSH and run the update from there.