There are two common causes for this to occur.
- If a flipbook is hosted on a secure website (https://), it cannot display insecure (http://). web pages that are added to the webpage feature.
- If your website prevents embedding in an iFrame then the Flipbook will not be able to display it.
You will need to add the origin domain (cloud.3dissue.com for example) in your X-FRAME-OPTIONS headers.