There might be 4 different factors that may be affecting the scan.
1. You QR code color is not contrasting enough with the background. Always choose high contrast colours for QR codes.
2. Your custom QR code information might be too long and therefore the QR code is too dense for your phone/scanner to read it.
3. You selected the wrong type of QR code.
So your testing with an app or scanner and you see a number instead of your contact's info?
You must likely selected the Eventbrite attendee ID QR code used for check-ins instead of the Contact Information (vCard) one.
Don't worry, just go to the editor, delete the QR code that's in the badge and insert the Contact information one.
Rescan and you should now see your contact's info.
4. The scanner your using is not compatible with QR Codes.
Tip: When scanning QR codes with mobile phones, keep the attendee's phone out of the sun or direct light.