Google Checkout question

I downloaded and installed the Google Checkout module, but it doesn't seem to be fully working.

The checkout button appears as it should, and it successfully submits the order to Google, but other than sending the order to Google, it seems to discard it - it never appears anywhere in the admin panel of the store, and I can't do anything with it outside of Google.

If I try to run responsehandler.php in a browser, I get a login prompt as the installer says I should, and I have the location of that script in my checkout seller account, with XML selected as the method.

If I check the message log, it's empty, so it definitely didn't receive anything.

If I check the error log, I see only a single failure from when I directly ran the script to make sure it got a login prompt.

I can't see any reason why it wouldn't work, but it doesn't.

If it matters, I'm currently running in sandbox mode, as I want to make sure this will work before actually letting a credit card get billed.