I can't close a text box in Settings on my new iMac

I tried linking my business email to my gmail. Unfortunately, it wasn't successful this time (I will try later). But the meantime, settings opened up a text box stating "Unable to verify account name or password". I have clicked on the OK button, but it doesn't work. I have to tried force close Settings, but the text box will not close. How do I get it to close? Screenshot shown for reference. Thank you in advance!