There are two types of currency in Gunner Z. ZMoney is the more common of the two currencies, and is primarily used for upgrades, while BX is used for extra continues on missions, as well as to speed up recovery and installation of new upgrades.
The main way of earning ZMoney is by playing missions. Whether you win or lose a mission, you’ll still earn ZMoney, but it’s recommended to play and replay the ones that you know you can beat, so that you don’t have to worry about waiting half an hour for your vehicles to recover because of losing. Your vehicle will be ready right away after a victorious mission no matter how much damage you took.
You get BX only from the missions that you win, not from the ones that you lose, so the above advice applies double for earning more BX. Plus, whenever you gain experience levels, you gain a whole bunch of free BX as a bonus.
Conserve your BX by using the time cheat to recover your vehicles and to speed up the upgrades. Set the time ahead in your phone or iPad’s settings to do this. If recovery takes 29+ minutes, set it ahead by 30 minutes. Then go back to the game and the recovery or upgrade (whichever one you are trying to speed up) will be completed.
You can get either free BX or free ZMoney by going to the in app purchase store, tabbing over to whichever one you want more of, and watching videos to earn free ones. Whenever you run out of videos, just wait a few minutes and more videos will be available. You can either earn 6 BX or 6,000 ZMoney per video that you watch.