Amazon.com can charge your Zip account in different ways. Especially if you purchase from an independent seller on Amazon. If Amazon charges you multiple times, and Zip only expects one charge, it can be declined.
First, make sure your Zip App is updated to the most recent version from the App store / Play store.
Next, make sure that your purchases from Amazon and your purchases from independent sellers are separated into different orders.
Finally, make sure the Requested Amount is high enough to cover any taxes or shipping charges. Don't forget that Amazon collects the sales tax of each different state.
If you have any questions or further issues, please contact us and let our team know.