Hi @email@example.com If you edit a post category you will see a box to set the ConvertKit Form for all posts in this category.
The Form chosen here will override the default Form chosen on the plugin settings page. If a post has multiple categories, and each of those categories have a Form assigned, the Form from the newest category will be displayed. Only one Form will be shown.
You can also check this guide: https://help.convertkit.com/en/articles/2502591-getting-started-the-wordpress-plugin29
I hope it helps. If you're still having issues or need further assistance you can always reach out to firstname.lastname@example.org.