If you get this Authorize.net error, it means that you need to add the URL of the page, where the payment is made, in your Authorize.net account.
Go to the Account → Response/Receipt URLs section of your Authorize.net account and add the URL there. This way Authorize.net will accept all payments coming from your order form.
If you use other URLs, you’ll need to delete them and add them again to the table. Start by deleting them all and including them again, one by one.