nova/doc/api_samples/os-volumes/v2.89/update-volume-attachment-delete-flag-req.json

{
    "volumeAttachment": {
        "volumeId": "a07f71dc-8151-4e7d-a0cc-cd24a3f11113",
        "id": "a07f71dc-8151-4e7d-a0cc-cd24a3f11113",
        "serverId": "fddf0901-8caf-42c9-b496-133c570b171b",
        "device": "/dev/sdb",
        "tag": "foo",
        "delete_on_termination": true
    }
}