Airdrop no longer moves files to my iPhone

I use Airdrop all the time to move audiobooks to my iPhone from my iMac. Today it is not working properly. Airdrop sees my iPhone, I can start the process and my phone sometimes shows the progress blue circle and appears to complete successfully and I get a double haptic vibe then nothing happens. Other times my iMac appears to be sending ok, but there is nothing from the iPhone end. What could be causing it to suddenly not work when it has worked fine for years? And the iPhone is ¾ empty so not full.

OK, I solved this myself. I shutdown the iPhone and restarted it and now it is working. I cannot see a way to delete this support question.