def METHOD_NAME(self, mock_get_store_signing_keys):
    mock_get_store_signing_keys.return_value = [
        {"sha3-384": "valid_signing_key"}
    ]
    payload = {}
    response = self.client.post(
        "/admin/store/1/models/Model1/policies", data=payload
    )
    data = response.json
    self.assertEqual(response.status_code, 500)
    self.assertFalse(data["success"])
    self.assertEqual(data["message"], "Signing key required")