: The emulator may detect the USB drive (e.g., via lsusb in a shell), but it is not mounted to a usable path like /mnt/media_rw/ . The solution is to use the PATCHFSTAB fix (Method 3.2) to modify the AVD's fstab.
Identify your device. For example, a USB Bluetooth adapter might have Vendor ID 0b05 and Product ID 17cb .