Happiness isn't earned or paid for, it's noticed. You can put yourself in situations where it's easier or harder to notice, but even if you put yourself in an easy situation there's no guarantee you'll feel happy. So instead, you have to practice noticing it.

The first step is just to acknowledge the times you do feel happy. When you're having a good time, instead of worrying about how it could be better, or distracting yourself from the happiness by worrying about other things, take a moment to say "This feels good, I'm happy to be doing this right now". Be present in your happiness.
Then you need to give yourself permission to widen the scope of where happiness can be found. Every rock on the ground around you can be a source of happiness, if you take a little time to learn how to look at a rock. Go pick one up, and pay attention to the details of its shape and coloring. Resist the thought that it's "just a rock", recognize that this rock is unique in its fine details, and pick something you like about it.

You don't have to pick something you think other people will like, this appreciation isn't about fitting in with anyone's expectations. It's a personal thing, you get to decide what makes a rock interesting or not. Even if your rules are silly or hard to describe, it doesn't matter, what matters is that you give yourself a system for enjoying the details of a rock.

Then drop that rock and pick up another. You're not collecting rocks, you're just looking at them. Repeat the process, find something you like about it. It's probably a bit easier the second time, right? It keeps getting easier. Now think about all of the rocks around you, each one has the potential to give you a tiny bit of happiness. That's a lot of happiness just sitting around in your environment, waiting for you!

Of course, rocks are just one small part of your surroundings. Trees, animals, buildings, people, sounds, weather... there's effectively an infinite amount of detail in the world that you can learn to enjoy noticing. The more often you do it, the more engaged with the world you become. You stop simplifying the world around you to the boring, stressful outline you're used to, and start reveling in the detail.

At the far end of this, when you get really good at it, you can even find happiness in sorrow, pain, and misfortune. I'm not a fan of my depression, but from a detached perspective I can at least recognize that it's kind of fascinating how part of my mind can be so effective at sabotaging my emotional well being. I've experienced shades of frustration or regret that are truly breathtaking examples of what a mind can do, even though I'd rather not have my mind doing that so often. When the world is grey and my head is screaming "this sucks, I hate this", I can at least buffer it with "but it sucks in an interesting way". You might be surprised to find out how quickly an antagonizing emotion will fade when it's met with curiosity and respect.