To Do items aren't being added with checkboxes
Here's how to add a To Do item (perhaps in an "Append Note" action) with checkboxes in OneNote.
Set the Content Type to "Html" and wrap the name of the To Do item in a <p> tag with a data-tag="to-do" attribute, like this: <p data-tag="to-do">item name</p>:
There are Sections in my Notebook but the New Note in Section Trigger does not show them.
This can happen if you are using Section Groups. We can only see Sections that have not been placed in a Section Group.
As you can see below, the 3 Sections I've put into a Section Group don't appear in Zapier. 