Help w/ Authorize.net Test

I don’t have a regular Authorize.net account yet, but I wanted to test the process so I did sign up and got a developer account for sandbox mode.

I’ve set up my system for sandbox mode with my API login/transaction key.

When I press “Pay with Authorize.net” – it takes me full screen to their website with the CC form. I put in my payment details and save and it sends me a receipt for purchase, but does not redirect me back to the callback, and doesn’t save my order – so my listing is perpetually unpaid in spite of having 2 receipts saying it is paid for twice.

What might I be missing here?