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. In these example screen shots from a computer and a phone, you can see the independent seller listed.
Last, make sure the Requested Amount is high enough to cover any taxes or shipping charges. Many of our customers forget that Amazon collects sales taxes in different states.
If you have any questions, please let us know.