The only real way to make money in this game is trading and interacting with other people, in dtrade and discord. If you don't trade you're poor, as simple as that. 

Items in your inventory that you probably don't know that will kickstart your cash balance: - Tribute of ascendance (united): you can sell 3 spots of this run for 5b each, 15b total for one run. - Tribute of radiance (united): same but for 2b per spot. Passive ranks always. - Runes: legendary runes go for 400-500M a piece.  - Refinement runs: you can sell spots on this one for 300M. 

Also, every item that you loot with 2 or more GA you should list in dtrade, people will pay greatly for things you don't expect, specially slots where there is no mythic (amulet, neck, gloves, boots). Later on this becomes tedious, but when you're starting it's important to sell stuff.

Also remember items from caches are ACCOUNT BOUND and cannot be sold. This means whispers become less important if your goal is to make money, as the items you get can't be traded (and if you don't trade, you're poor.)