def METHOD_NAME(self, mock_get_store_signing_keys):
    mock_get_store_signing_keys.return_value = [{"sha3-384": "valid_key"}]
    payload = {"signing_key": "invalid_key"}
    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"], "Invalid signing key")