Your PAN card should have 10 digits and be alphanumeric.
You might need to re-check that the PAN number that you have entered is in the correct format without any spacing or special characters, and that all letters are input in uppercase.
Please make sure you have entered the number exactly as it appears on your card.
If you’re still having trouble registering, please try clearing the browsing history of your device and using a different browser and/or device (eg. Desktop PC, tablet, mobile phone, Google Chrome etc.)?
If you follow the above-mentioned steps, this should let you bypass this issue.