can't buy funds

This seems indeed like an error, however the payment portal is maintained by EA. I'm afraid I can't help you much more than pointing you to their helpdesk. They usually are quick to resolve issues with people unable to purchase.
https://help.ea.com/en/contact-us/?product=cc-tiberium-alliances&platform=browser&category=orders&issue=unable-to-purchase&isChannelSelection=true