Error when using Authorize.net Accept.js

[LauraS]

I set up Authorize.net Accept.js using the instructions under Setup in the documentation . I then attempted to place an order using it and the customer's information was added to Authorize.net, in their CIM section, but the payment part of the transaction failed. The Gateway Transaction Log reports the following:

Invoice ID => 23456
User ID => 3
Amount => 10.00
Error Code => 33
Error Message => Invoice Number is required.

Is this a software problem (a glitch) or a "me" problem (something I may have missed)?

Thanks, in advance, for your help!