If you run in to any issues printing transactions on the backend, there are a few things you'll want to check for if it looks like your transaction is not opening.
Check Browser Windows & Downloads Folder
Novi doesn't actually directly print invoices. Instead, we generate a PDF that any browser can print. This means that while some browsers may open this transaction in a new window or tab, others may send it directly to your Downloads folder.
Check for Popup Blockers
If it looks like "nothing is happening" when you try to print a transaction, check your pop-up blocker and make sure that pop-ups are allowed. If it already does, add your website URL to the list of trusted sites.
A quick Google search should return articles for your particular browser. Here is an article explaining how to allow pop-ups in Chrome.
Chrome will also provide visual queues if it is actively blocking a pop-up from a website.
Clicking on the icon will allow you to quickly approve pop-ups specifically for your site.
Try Another Browser
Different browsers can be configured differently when it comes to this type of download. There is a chance that you will find luck with another option. Try Chrome, Safari, Firefox, Edge, or even IE.