What is the exact error message?
Would you be able to try the app instead of a browser (or vice versa) and/or another device/browser to see if the problem persists elsewhere?
You might need to contact 48 support about this.
See the link in my signature below or email them at support@48months.zendesk.com
Fow what it's worth, I don't seem to get that problem when I go to buy a membership so it may not be a system wide issue but specific to you/certain users for some reason.
