Often times on a WooCommerce site you may come across a checkout or product issue when using Event Tickets Plus. Typically this is related to using the built-in Tribe Commerce option for processing orders rather than WooCommerce.
For all WooCommerce sites we need to make sure they are not setup to use Tribe Commerce. Switching from Tribe Commerce to WooCommerce is a pretty straightforward process and luckily The Events Calendar team has a great guide on how to fix this issue.