The best thing you can do at this time is remove the software and then perform a reinstall. If this is not happening, download the latest version from the official website and try that.
Official website: https://nos.nprotect.com/landing/woodhuston/
In case this solution isn't viable to you, then you will have to contact the developers:
Toll-Free : 1-855-466-7768 (1-855-GO-NPROT)
Office : 1-408-477-1742
E-mail : support@nProtect.com
Additionally, try changing browsers to pay again. This could also be a compatibility issue with one of your browsers or settings in a browser.