Make sure you have followed all the troubleshooting instructions as described above and here https://youtube-downloader.uservoice.com/knowledgebase, if you still have any issue other then these, email to your PRO payment email.

Usage of this website and all provided products is subject to compliance of your countries legal permissions, if your local laws do not permit downloads and audio conversions of online videos you are not allowed to use this service. You are also not permitted to use this utility to infringe any sort of copyright by downloading multimedia content which you don't have rights to use or is not open-source.