You shouldn't need a USB 3.0 drive... a USB 2.0 will work, you just have to have it formatted correctly.

Put the flash drive in your PC and go to Computer, then right click on your flash drive; select Format. In the File System type, select FAT32, not NTFS. This will erase everything on the drive so you'll want to back it up first if there's anything you want to keep. Once it's done, it should be recognized with your PS4.