Apple Jelly Not Setting

I just went through a nightmare! I made 4 different batches using different pectins. I then found out that because I was using juice that was my problem. Apples only have natural pectin in the core and peels, and so using juice makes it difficult to get it to jell properly. Adding lemon juice helps. I have yet another batch that I plan to experiment with tomorrow.
I will never attempt jelly from juice again, Its always best to cook apples (core and all) down and use the juice from that.

Use pectin that you buy in the store. Certo is the brand that I use, but there is a store brand as well.

Several years ago I made some mulberry jelly that didn't jell. I didn't want to go through the whole process again. Sooo...we had nice mulberry syrup for our pancakes. Apple syrup sounds pretty good. Try it.
Margaret from Denton, Texas

Some of my jelly didn't get thick enough this summer. When I open a jar I stir in a small amount of Instant Clear Jell which I bought at a local bulk food store

Pectin is made from green apples. Did you have any in it?
Boil it longer is only thing I can think of, to concentrate the pectin.