Investment (5e Variant Rule)
From D&D Wiki
This is a variant of running a business which makes guaranteed, but limited, profit. Basically, it just converts DT into GP at a 1/1 ratio, which is far less than can be earned by the gambling options of the core rules activities. It's also a horrible waste of time unless the PC truly values GP over everything it could be used to do. I mean, really, by doing this, they're making it harder to spend their money, and simultaneously collecting more money, which means they're only doing it so that they can have a big pile of money. If they aren't doing anything with their money anyways, what does a few more coins on the heap matter? Let them be Scrooge McDuck.
The fluff of this downtime activity is that the character invests their money in a business, writing a contract with that business owner to pay out a small portion of the profit, and requiring a full return on their principal at the end of the contract. This equates to a profit of 1gp per day spent on this activity. Note that a player must still cover their lifestyle expenses during this activity, so if they are foolish, it may in fact have no impact on the game whatsoever outside of establishing their character in the community.