We set up a custom post type with a custom taxonomy and realized that Authors were unable to add new terms.
This took a bit of googling and trial and error so here is a good way to allow authors in WordPress admin area to add or edit taxonomy terms that can be used with posts or custom post types.
It’s as simple as adding a new capability. Here’s how we did it.
Install Members Plugin to manage capabilities on a per role basis.
Edit the respective role, for us it was the Author role that was missing the capability to add new terms.
Add a new custom capability assign__terms (copy and paste to get the correct double-underscore character)
assign__terms
That’s it! Save and you should be able to test your author role can now add categories or custom terms to the custom taxonomies in the WordPress admin area.