I have an iMac with IOS Sierra two iPhones with the latest IOS and an iPad Air with the latest IOS. If I want to AirDrop a photo from my phone or iPad to the iMac, it works flawlessly. When I try to send from my iMac to the iPad or iPhone, it gets stuck on "waiting" and after considerable time it fails. I am using the same settings on all devices. When I try a Mac to IOS device Airdrop the device shows up immediately. I tried restarting the iMac. I'm stumped.