So running a new install of Magento 2.1.7. SSL is in place. Paypal and other payment methods seem to be working fine. However, with standard credit card payments via the built-in authorize.net API, I'm getting this problem even on legitimate credit card numbers. Sometimes it also complains about the expiration date when I actually hit "Place order." The order is never passed on to authorize.net as I can't get past this javascript checking. This is also true even when I turn off "Credit Card Verification" in the authorize.net payments section of the store config. Any ideas why this is happening?
Also, Noob alert.