ios - '__' is not convertible to 'StringLiteralConvertible' -

i don't understand why code producing error:

alamofire.request(alamofire.method.patch, "https://example.herokuapp.com/", parameters: [             "format":"json",             "todo":                 ["iscomplete":todo?.iscomplete],             "id": todo?.id // <--- error: not convertible 'stringliteralconvertible'             ]         )