I just paid for the program and I still keep getting error can't download on 4k downloader.

I downloaded the newest version of 4k downloader 3.6 and the program was working good for a while but then it stop working out of the blue. It says Parsing then i'm able to pick what quality to download the video in but once I hit download it goes to the message Error : can't download. I then went and paid for the 4k downloader thinking it would work better but it still brings up the Error : can't download. I need help I really like the product and I would hate to get a refund.