People have short attention spans online. They might be interested in coming to your event, but if they can't easily figure out how to make a purchase on your website, it's on to the next thing.
Even if you have a link to your Webtix page in your site's navigation bar, make it really simple for your patrons by adding a nice, big, bold "Buy Tickets" button.
As you can see from the example below,
The Little Theatre on the Square
has a very prominent "Buy Tickets" button surrounded by lots of white space. That makes it very easy for their patrons to just point, click, and buy.