I’ve been trying to figure out how to loop this animation where a coin is spinning, but when I add the animation in-game, the coin just spins in a full 360 degrees and the stops and I get the error “AnimationEvent has no function name specified”
Set also the default animation and at the Wrap Mode dropdown select loop.
if you click on the animation there should be a drop down menu you can then select either loop or ping pong I think ping pong would work best for this coin of yours. Hope this helps
The “AnimationEvent has no function name specified” error is because you clicked the animation event button by accident (most likely) instead of clicking the keyframe button. Animation events make function calls. So it it trying to figure out what function to call when it hits that frame.
Drag animation in Hierarchy > click on your animation in Assets > open elements of animation (by clicking on arrow on it) > simple drag animation video (you will see icon with play button on it) in Inspector section of your animation | you will see that you now see name of that clip in Animator section > Controller. Your animation is loaded when you hit play it plays once.
Now above you got Model section with Select, Revert, Open > click on Select > you will find Loop Time click on that > start animation and you got infinitive loop 
Select the animation file, then in the inspector panel have a tab (up) , right click on this tab and select “Debug”. Then you see the “Wrap Mode” too.