Unable to attach a cloned boot volume?

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I created a VM. Now I want to make the boot volume larger so I created a clone boot volume first in case something goes wrong. I cannot figure out how to test the cloned boot volume. I stopped the VM and detached the original boot volume. Now on the Boot Volumes console page, clicking on either the original or clone, then clicking "Attached Instances", then clicking the blue "Attach to Instance" button only shows me one of many VMs in the compartment, and it's not the VM where either of these boot volumes came from. Why can't I attach the clone boot volume to the same VM where it was originally created? Thanks in advance for any explanations or pointers to relevant documentation.