macbook music to iphone "add to device" not working
I have transferred many files recently from my MacBook Pro (Retina, Mid 2012) running Catalina 10.15.7 to my Iphone SE (1st gen iOS 15.7.6) with no problem. But all of the sudden, when i right-click a song, select "Add to Device" (my iphone is plugged in and recognized), i get the spinning wheel at the top of my iphone indicating it's happening but songs never appear. I have plenty of space on my iphone. I do NOT have ICloud Music Library on, nor do i have "ITunes Match." Music on Macbook is up to date (1.0.6.10), Iphone is up to date. And I have "MANUALLY manage music checked in Macbook Music). It was working fine the other day, then ....
I've also restarted both my phone and Macbook.
iPhone SE