There are some limitations as below:
You can't move a VPN Gateway that is associated with a Standard SKU public IP address to a new subscription. Azure Public IPs are region specific and can't be moved from one region to another.
Some resources aren't supported to be moved, but a Public IP is.
Before you move the Public IP, make sure its dissociated (unattached) from a resource.
Then once dissociated, you can trigger the move.