Limit number of posts under a post type?

In order to enforce your post limitation until the user pays the license, I suppose you should check if limit is reached when:

1. user clicks on “add new”
2. user displays list of current entries

AFAIK, the way to do that is to use the relevant hooks but that depends a bit of the user experience you want to create.

For example, if you use the action hook publish_post, you could force the “draft” status of the post until the user has paid.

See the full action hooks list here.