Can't pop ears

I am trying to get into freediving and so I have had to practice popping my ears. However, I can never get them to pop. The only thing that ever happens is that something kind of bubbles out after I blow. Sort of like when you barely open a soda can vs when you pop it open in one smooth shot. I tried some ear wax removal drops but it's not reacting with anything so I'm assuming there is no wax build up like I originally thought. I used to be able to pop my ears years ago and have never really had to do so since. But now I can't and cannot figure out what's wrong or what to do. Any suggestions?