I killed a couple tanks, got some money, but eventually lost all my hearts. Is there a shop where you can buy hearts? Is there other enemies, or any other content in the game that I might have missed?

I cannot find to earn money.

Yeah, some instructions on how to play the game would be nice to have. I haven't managed  to know how to shoot :)   You  can add it on your game itch page.

I liked the sound though,  the game has nice back music, sound of gun shots is funny  :)  It was    surprising  for me that teleporting costs some money, probably you should add some note, like you did it with the sellers

Really nice game loop. The first time I bought a red laser which did not turn out well. Like the multiple zones and earning better lasers. What did you make it in? You can also add instructions to the itch page without affecting the jam submission if you want to make the onboarding a bit easier.