iOS to Mac
If you are having trouble AirDropping to a Mac from an iOS device – like I do frequently and randomly – then it may be that for some reason your Mac’s Bluetooth connection is not “visible” to the iOS device. There is a way that should force the Mac to reveal itself to your phone / iPad. In the menu bar click the Bluetooth icon and select “Open Bluetooth Preferences…” A System Preferences window will open, leave it open and try the AirDrop again.
Hopefully you have Bluetooth visible in the menu bar, if not just open System Preferences and select Bluetooth.
Mac or iOS to iOS
If you can’t find your iOS device as an option in AirDrop maybe Do Not Disturb (DnD) is on, if so that will deactivate AirDrop. The solution is to turn off DnD : ) If DnD is active a crescent moon will display in your status bar, you can deactivate it by pulling up Control Centre and tapping the crescent moon icon.