Authorize.net not connecting in Craft Commerce?
That error is from the cart service when trying to set the payment method ID on the cart during payment.

There are 2 possible reasons the error would appear:

1) The payment ID you are submitting is wrong

&lt;input type="hidden" name="paymentMethodId" value="theIDhere"/&gt;


2) In the settings (for a correctly submitted payment ID), the "Enabled to select on front-end" setting has been turned off. Screenshot: http://jmp.sh/AxoM1tI You need this on, to allow customers to use the method on checkout.

Hope that helps.