what you call tip layering sounds like you did a cutting, not layering. Try layering this way: choose a branch close to the ground, cut part way (1/4 to 1/3) through it, and pin it to the ground. Pin it so as to make sure the cut is open, so it doesn't heal over. Leave it for several months at least, as they are very slow to root.

I am assuming by air layering you chose a branch higher up, wounded it, then wrapped it in peat moss covered by plastic or foil. This is what I know as air layering--done away from the ground. Callous usually forms before roots, so perhaps you just didn't wait long enough.

If you try cuttings again, take them from down low on the plant, and put the pot into a plastic soda bottle (cut off the top of the soda bottle, put the pot in, then tape the top of the bottle back on). This will provide plenty of humidity to keep the cutting from drying out. Remove the cap of the bottle every once in a while for a moment or two to let air in. You should not have to water the pot at all, the bottle should keep all the moisture inside. You need to be patient because they can take several months to root. The bottle should be keep in bright but full shade--letting any direct sun hit the bottle will roast the cutting inside it.