Can't access the clipboard and/or paste in a particular application

I use Choosy to open particular URLs with particular browsers. I discovered I didn’t have it installed on a secondary Mac today, so I installed it, and while trying to paste my serial number in, I discovered I couldn’t paste it. I quit the app, restarted etc., confirmed pasting worked between other apps, but never figured it out. Now, I am on my primary Mac, and I wanted to edit a rule for Choosy and discovered…I can’t paste the URL into the app. So this is the same behavior on two different machines and I’m not sure what gives here.

Anyone familiar with the app or this behavior in general have any ideas? Is there a permission somewhere in the system I need to enable to allow pasting from one app to another? Any ideas/suggestions would be welcome/appreciated.