This usually happens because of cache plugins, try clearing cache plugins, and deactivating the cache plugin.
Also make sure your checkout page have the required Easy Digital Downloads shortcode.
There are 4 pages you need when using the Easy Digital Download plugin. If for some reason you accidentally delete one of these pages, below you will find the page title and the short code that is needed on that static page.
Shortcode & Settings
Your transaction failed, please try again or contact site support.
Thank you for your purchase! [edd_receipt]
Beat Store Settings
Make sure you select the pages you created under the Beat Store Settings tab.