Maybe you're trying to propagate a plant species that just doesn't root easily. What are you trying to air-layer?

I'm trying to air-layer vietnamese guava. hopefully it will take.

No experience air-layering guava, but there are numerous YouTube videos on that. Make sure you put tin foil or something surrounding the layer to shade it from sun, as full sun can cook it.

I tried rooting cuttings of guava in fall and winter and had no success. Most likely there was not enough heat and light, so I'd probably do better in summer. But you may have success with that method if you live in a tropical region with high humidity and consistent warmth. Make sure you limit leaves to 3 or 4 per cutting and cut the leaf surfaces back halfway to reduce transpiration during the rooting process.

https://www.youtube.com/watch?v=RPqnGtZDKUg

Thank you!