WordPress GetPaid plugin: low-privilege users can read and alter invoices

The GetPaid plugin for WordPress before 2.8.63 contains an incorrect authorization vulnerability where the check_post_permissions() method in includes/api/class-getpaid-rest-posts-controller.php maps REST operations to generic WordPress post capabilities instead of enforcing the plugin's manage_invoicing permission. Authenticated users with lower-privileged roles such as Editor or Author can exploit this flaw to list other users' invoices, mark pending invoices as paid without recording payment transactions, or create published items and new invoices through the REST API.