Are you sure you don't already have it applied, which is why you can't click on it?
If not that, maybe try reloading UI?
I have seen this happen a number of times before, and have yet to see a case where one of the above didn't fix it.
Not really sure, I think it's just maybe a sporadic thing, like how sometimes a random attuned crafting station won't work till reloading UI.
Glad it works now!