The EPUB3 files that CircularFLO produces can be validated automatically as part of the process. We use the free tool pagina EPUB-Checker to do this.
As the creation process with CircularFLO is automatic it is rare that an EPUB will not validate but if it does then you will be alerted and the report will be shown in EPUB-Checker. There is usually a simple reason but unfortunately the simple reason might be hidden in a scary looking report.
This site helps to decipher what the report means. The most common reason we find is a ‘required elements missing’ error caused by hyperlinks pointing to none existent page.
If you are having trouble understanding a EPUB check report then please feel free to send the EPUB and the report to us.