The Micropub spec now requires HTML content be sent as a nested object, content[html]=<b>example</b>.
You can read more about the change here.
When you are ready to receive the content as an object, click the button to switch.
Clicking "Publish Now" will send a request to your Micropub endpoint.
The request will include two fields, "name" and "content", where the content will be the full HTML for this post.