Pro applies to charts you create or refresh after activation. It cannot change an image, file or share link you already made.
Check that the header badge says Pro. For an inserted picture, reopen it and choose Update this picture, or use Update all charts for a workbook. For a file or share link, export or share the chart again.
If activation fails, check the key in Settings & license and your internet connection. Use Your account or contact support for license help.