Yes, unlike most credit card processors, you can take payments in an offline mode. there are some caveats though. you must connect the device that took the swiped transaction (you can use a chip card in offline mode) to the internet within 72 hours of the transaction. You will be responsible if the card is declined to get payment from your client so take their name and phone number to be able to contact them for repayment.
see this article for all the details.
https://squareup.com/help/us/en/article/5095-process-payments-with-offline-mode
