Investments
Source GM Core pg. 49
The downtime system isn't meant to deal with investing credits, receiving interest, or the like just to make more credits. Rather, investing should result in changes in the universe. PCs might invest in founding a museum and find on their return that the collection has grown. If they fund an expedition, they might get access to interesting trade goods later on.
When characters are investing in a major endeavor, the amount of in-world time invested often matters more than the credits. While spending additional credits greatly increases the efficiency of Crafting an item, you can't build a shopping mall in a day just because you have enough money to pay for the whole process. Downtime is a good opportunity for characters to start long processes that can continue in the background as the PCs adventure, provided they can find a trustworthy, competent person to run things in their stead.
When characters are investing in a major endeavor, the amount of in-world time invested often matters more than the credits. While spending additional credits greatly increases the efficiency of Crafting an item, you can't build a shopping mall in a day just because you have enough money to pay for the whole process. Downtime is a good opportunity for characters to start long processes that can continue in the background as the PCs adventure, provided they can find a trustworthy, competent person to run things in their stead.