API feeds is to pull data from Micro.blog - for example replies. To enable cross posting from your existing blog, a setting can be enabled. From the help page on getting started [1]
> "If you already have a blog, such as one based on WordPress, connect it to Micro.blog by adding the feed URL to your account under Account → “Edit Feeds”."
> "If you already have a blog, such as one based on WordPress, connect it to Micro.blog by adding the feed URL to your account under Account → “Edit Feeds”."
[1]: https://help.micro.blog/2017/getting-started/