Square > Payment Error: Card nonce already used; please request new nonce

What does this error mean? 

I am not sure. I never saw that error message before. I searched on the internet the message you provided and I only found this Square thread - https://www.sellercommunity.com/t5/Developer-Discussions/Card-nonce-already-used-please-request-new-nonce-message/td-p/112427

Did you previously enter the wrong credit card info?

Please try to submit the form again. You can also try to use a different browser or device.