You can use the REST API to add sub-issues to issues. Creating content too quickly using this endpoint may result in secondary rate limiting. For more information, see "[Rate limits for the API](https://docs.github.com/rest/using-the-rest-api/rate-limits-for-the-rest-api#about-secondary-rate-limits)" and "[Best practices for using the REST API](https://docs.github.com/rest/guides/best-practices-for-using-the-rest-api)." This endpoint supports the following custom media types. For more information, see "[Media types](https://docs.github.com/rest/using-the-rest-api/getting-started-with-the-rest-api#media-types)." - **`application/vnd.github.raw+json`**: Returns the raw markdown body. Response will include `body`. This is the default if you do not pass any specific media type. - **`application/vnd.github.text+json`**: Returns a text only representation of the markdown body. Response will include `body_text`. - **`application/vnd.github.html+json`**: Returns HTML rendered from the body's markdown. Response will include `body_html`. - **`application/vnd.github.full+json`**: Returns raw, text, and HTML representations. Response will include `body`, `body_text`, and `body_html`.