I'm using Zoho Books with Google Checkout. My invoice status is not updating when an invoice is paid.

I'm using Zoho Books with Google Checkout. My invoice status is not updating when an invoice is paid.

I have been using Books for a few days now. I have set up the API callback set up properly I think. I had a customer recently pay his bill, but the status of the invoice says it's now one day overdue. You can see how frustrating this could become if my clients start getting reminders for bills they've already paid. Can someone please help me figure this out?