@Charles Terra only supports older style USB 2.0 sticks, newer USB 3.0 won’t work. Also the stick needs to have an MS-DOS FAT file system on it. You can check the file system by right-clicking the drive and selecting “Get Info” from the context menu. To change the file system, you need to erase the stick. With the stick plugged into your Mac, open the Disk Utility app, select the drive to the left, then hit Erase in the toolbar, then select “MS-DOS (FAT)” from the Format menu and hit “Erase”.
