Credits is the game’s main currency which you’ll need to buy Weapons, ammo, explosives, or pay for your Bike maintenance. You can get most of it by completing jobs and missions. You can also earn a bit by collecting ears from freakers and turning them in as bounties in encampments.
Harvesting wild plants and Hunting animals for Meat will also allow you to donate them to an encampment’s Kitchen in exchange for a small amount of credit and trust points.
The amount of credits you have accumulated will depend on the region. For example, by doing missions and activities in Hot Springs, you managed to earn 13,000 credits there while you earned 5,000 credits by completing missions in Cascade region (Copeland's Camp). That said, the 13,000 credits you owned will only be honored by the Merchant and Mechanic in Hot Springs and when you travel back to Copeland's Camp, you can only use the 5,000 credits you've earned there. You can check the credits you have by accessing the inventory screen and looking at the lower left corner as shown below.
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