Kambo without purging happened to me in the beginning a few times. Most of these were due to not enough dots, or not rubbing the skin layer away well enough. Dots should appear as pinkish white spots after burning and rubbing, which means that the layer of skin has been rubbed away. This makes a lot of difference.
Another thing is drinking enough water. When you get close to gulping down 2 liters, the sensation of wanting to throw it all up becomes very acute. If you don't get this, maybe drink some more water?
Besides that it still can happen that a purge stays absent. One of the things I learned was that once you get accustomed to kambo and have purged on it a few times, you get a sort of association between applying the kambo and vomiting shortly after. Nowadays vomiting follows naturally after applying the dots.
It brings great relief once you start purging. Actually it's the only desire on my mind when the kambo kicks in, to throw it all up

. I also keep some water during the purge, when vomiting becomes strained, the sensation you're stomach is running empty, I quickly empty another cup of water to keep on purging...
Hope this may be of some help...