WHMCS checkout not completing transaction when "complete order" is clicked

Hi there!

I'm testing the shopping cart and have tried to complete some test orders. for hosting. When I click on "Complete Order" the button says "Please Wait...", but nothing happens. No error message, no spinning wheel.

I retested directly in the WHMCS install and the order completed without issue and I was emailed a receipt. The issue is only occurring in the Wordpress integration.

I also tested in a couple different browsers. No go.

Got any suggestions?