I believe it is just "policy_id". As an incomplete example the specification via API would be something like:
{
"cluster_id": "1234-567890-abd35gh",
"spark_context_id": 1234567890,
"cluster_name": "my_cluster",
"spark_version": "9.1.x-scala2.12",
"node_type_id": "Standard_DS13_v2",
"driver_node_type_id": "Standard_DS13_v2",
"spark_env_vars": {
"PYSPARK_PYTHON": "/databricks/python3/bin/python3"
},
"autotermination_minutes": 25,
"policy_id": "D901239DSFKJ43234"
}