Indeed the inAudible application is no longer available. I've searched the web and all the available websites, and although there are traces about the software, nothing exactly could be found in terms of troubleshooting, user guides, downloads, etc.
I've also checked the application page at Software Informer and the outcome is the same. There is a page on the Github website that handles the remaining inAudible functions like (DRM removal, license retrieval, etc). You should check it to obtain additional information.