If you received an error when trying to purchase a zyBook that contains the words "Card declined", you should first check to make sure that you typed all of your information correctly. It might help to clear out all of the fields and retype them.
If you are still having trouble, this may mean that your bank does not approve of the transaction. In that case, you should reach out to your bank to learn more.
In the meantime, please feel free to request a temporary subscription by following along with the help article, Does zyBooks offer temporary subscriptions?
If you are still having trouble, you can contact email@example.com, and our support team can assist you with further troubleshooting. In some cases, we may need to refer you back to your bank.