The pot is way too big. I suspected it was going to die from your very first post (although I hoped I was wrong). Young JMs are extremely sensitive to being in huge pots because they drain too slowly for that itty bitty root ball.
Now the roots are failing, which is why the foliage is drying up. I'm not sure if you could salvage it now, since the tree likely used up its last remaining energy on leafing out.
If it were mine, I would attempt to "slip pot into a much smaller and much taller pot" (if that makes sense) with well draining soil on all sides of the existing root ball, while being as careful as possible not to disturb it as much as possible.
Resist the urge to let it dry out to fix the problem--the foliage actually needs more water not less. So do a regular watering routine, making sure that water is running freely out the bottom. This is very important for sucking air into the root ball, which is what you need to have a chance.
Best of luck.