If a user starts a ticket order on an event page -- choosing ticket quantities and proceeding to the donation page -- but does not complete the payment on the donation page, their order is saved in the site cookies. This means that if they go to an event page on your site in the future (same event page or different event) and choose tickets, it will just add it to the previous order instead of start a whole new order. This can cause confusion for users who start to buy a ticket for one event and then decide to buy a ticket to a different event instead. They might get to the payment page for the second event and find that it is about to charge them for tickets to both events.
The solution to this problem is to add some code to your website's custom theme so that any pending ticket orders are cleared automatically when a user visits an event page.
To make this adjustment, you will need to be using a custom theme for your website. Once you are using a custom theme, you should place the following code in the Layout.html file of that theme, just above the closing </head> tag:
NOTE: You will need to replace 'slug.nationbuilder.com' with your site's URL. If it is not the primary site, be sure to include the site slug. For example, in my nation I replaced 'slug.nationbuilder.com' with 'detroit-brianpalmer.nationbuilder.com' because the site that I am editing is not my primary site, 'detroit' is the slug of the site and 'brianpalmer' is the slug of my nation.
And that's it! Now when users visit an event page on your site and already have a ticket order pending, it will clear the order and the page will reload on the same page.
Complete and current information on how to use NationBuilder is available in the documentation section.