verifies but doesn't open?

I downloaded and when I try to use it, a verification box pops up, and never seems to finish. Has anyone else had this problem? Is there a way to fix it?

Supposedly the OS information that you have omitted is macOS. It has been reported that “never” is actually a very long time required for this task for some reason, so long that it might need overnight. It is only required once (they say - I don’t use macOS).