amex authorize blank check click code contact credit declined error invalid net number page returned

On the Amex, it's just a blank page that says:

3

6

The credit card number is invalid.
Click here to go back

And when I go to check Authorize, it never even shows up as declined, so I don't think it's even getting that far.

That error is being returned by Authorize.Net

"3" is their "Response Code" and it means error and "6 The credit card number is invalid" is their "Response Reason Code"

You need to contact them.