What is the correct way to define a subtype in Flow?

In the following code example, the intention is that scrapeMovies function accepts only serializable objects.

/* @flow */

type SerializableObjectType = {
  [key: string]: string | number | boolean | $ReadOnlyArray<SerializableObjectType> | SerializableObjectType
};

type GuideType = {|
  rid: string
|};

const guide: GuideType = {
  rid: 'foo'
};

const scrapeMovies = async (guide: SerializableObjectType) => {};

scrapeMovies(guide);

https://flow.org/try/#0PQKgBAAgZgNg9gdzCYAoVAXAngBwKZgDKeATgJYCGMZAXhQEYx4Dy9AVngMYYAquBAXjABvVGDABtANZ4sALjABnDOQB2AcwC6C5WvVgAPmFUBXALb1ShsPThwmFVdYAkAJTwUAJs1UwsAQRISCiwAHmJyKloGJlYObj58AD5rCMpqOkYWdi5eflQAXwBudGx8MABxEzJPPETBEQMxMHJPHRUyDVQDYvROOFVlMHVq2oUqmrr+MCFRcVaFAHIoO0XCktR+wYwlTmD8AFk4ADcyPEUZsApFLFVOMAAKEcmFNKjM2JyE-gBKGZThL1UIo9hRDiczoonqM8D8ikA

I do not comprehend what is the reason flowtype is complaining about scrapeMovies being fed guide object, which is less strict definition of a SerializableObjectType.

Whats the correct way to define a sub-type here?

from What is the correct way to define a subtype in Flow?