QR Code widget: allow the codes to be scanned once only

i have added a QR code to this form. can they be scanned and marked as scanned. We are working on entry tickets with each code only to be used once on

Unfortunately, it's not possible in the widget. The widget can be scanned by anyone who uses the form. There is no option to limit the QR Code data. 

You may consider sending the codes to your clients then enable the Unique Question Limit in the form. 

https://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question

When enabled, your clients can only submit the codes once. They'll be prompted with an error if they re-submit the same codes.