This is the spackling I have:
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Forget the spackling.
Fiber joint tape should never be used in a corner - use Paper Joint Tape instead. It has a seam down the middle, so you can fold it into the corner.
Scrape out the old joint tape, removing any loose compound along the way. Ensure both surfaces are securely attached, to their framing members. Sand any high spots if needed and apply paper joint tape in it's place.
You can use an Inside Corner Trowel to aid in making a smoother joint, while having fewer steps between coating and drying.
If it is a long run, you don't have to do it all in one shot either.
90 minute Lightweight Setting-Type, works great for repairs like this, due to a stronger joint, and quicker turn around while working. You just mix up what you need, and as long as you keep the remaining unmixed powder dry, you can store it for quite a long time.
This wall to ceiling joint appears to be due to stress on the joint caused by a combination of wall board movement due to environmental changes and a lack of sufficient drywall mud installed over the fiber joint tape in the first place.
I suggest that the best fix for this it to actually attach a new layer of the fiber joint tape all along the joint and then applying new feathered out layers of wall joint compound along the upper wall and out along the ceiling edge. After drying and sanding prime with good primer and re-paint the room.