Whenever you visit any of the stores in Dragon Ball Z: Kakarot, they require you to pay for the items using Zeni, the main currency of the game. Unfortunately, the majority of the missions in the game do not reward you with Zeni. They usually give you Z Orbs, D Medals, or ingredients to use to cook high quality meals with a cook.
The best way to make Zeni in Kakarot is to sell items that you find in the world. These can be rewards you receive from side missions, hidden items you find while traveling the world, animal parts you receive after catching them, and many more. You want to make sure you're selling valuable items, not crafting materials that you need to make recipes or craft machines.
In the description, you can say the item above; a beast horn can be sold at a store for a low cost. However, it does not contain any details that qualify it as Development Material, Gift Item, Event Item, or with associated status effects. You can sell it at any store and receive a significant amount of Zeni.
To farm these types of items, you want to explore the world and hunt down any creatures you come across. You can find dinosaurs, fish, deer, gazelles, wolves and many more. You won't always get items like these, but if you capture enough, over time you will find things for sale in a store. You should also check out the gifts section, as some of the items further down the list don't upgrade any of the Soul Emblems. Instead, these are high quality items that you can make a big profit from in the game.
Your best bet is to complete any of the side missions you come across and hunt down any animals you find. The more you do this, the more Zeni you'll have in your pocket.
