Sounds like you have a previous Pending charge that has not been paid yet. To see what that could be use the steps under the section titled "How to see your purchase history on your device" in this Support Article.
View your purchase history for the App Store and other Apple media services - Apple Support
You may need to adjust the filters to view all transactions. In the Screenshot on that Support Page, the example shows only the "Last 90 Days" and "Paid" transactions. Any amount in Red is listed as Pending has not been paid. You won't be able to make additional charges until any previous charges have been paid.