It seems that you're using an outdated browser. Some things may not work as they should (or don't work at all).
We suggest you upgrade newer and better browser like: Chrome, Firefox, Internet Explorer or Opera

×
So I filled the standard APO, but can someone tell me how I do buy slots? Checked controls but just found the buying-keys to fill the slots.

Thx for the help
This question / problem has been solved by Muyfa666image
You need to find extra slots on the maps while playing. Took me awhile to find this out too.

A good place to find slots are in group 5, level 3. There are slots for all APO at the pipe that are below the wooden bridge at the center of the map. Also, in the opposite direction, there's a extra slots all around on a beam you can drive up on. There are lots of powerups in the southwest lake, and even more if you follow the underwater pipe from there. Really easy to level up if you repeat this level a bit.
Extra slots look like blue square icons floating in the air, turning around. You need to drive over them. Some are more easy to reach than others.

I think each level has these, at some place.