This guide outlines troubleshooting steps when an external drive or SD card doesn't show up in the Files app on iPhone or iPad.Force quitting the Files app and restarting it generally brings the connected drive to the Locations list.Check the connection of the external device and ensure the adapter doesn't require too much power for iOS device port.Disconnecting other devices and restarting iPad or iPhone helps resolve temporary bugs or glitches.Reformatting the external drive into a file format supported by Apple may also help.Check mobile device compatibility with external storage devices to avoid hardware being incompatible with the mobile device.Update the iOS device to its latest Software Update to fix any system bugs causing the issue.Deleting and reinstalling the Files app or resetting all settings is the last resort in resolving the issue.It is recommended to match the external storage device with the mobile device model, MFi or works with iPhone certification or a similar mention.Additionally, reading the external drive's manual or contacting the manufacturer for assistance can be helpful.