4k video downloader not working after purchasing license key. Have restarted mac, to no avail.

The program allowed me to make, i think, 25 downloads, then had to buy a key. Which I did. Once I loaded the key, as requested, the program does not work anymore, when i paste the web address of a clip, it simply days it can't download it. Even a clip I downloaded before I got the key is the same. I've restarted my mac, still the same.