What Solari buys
Solari is Dune: Awakening's currency. It pays for taxis between hubs, vendor schematics, vehicle parts and anything other players list on the Exchange, the player market inside the CHOAM Exchange where prices are whatever your World will pay, not what a vendor sets.
Why it's slow to earn
Coins drop when you die, so every haul ends with a 500 Solari taxi to a social hub and a deposit at the bank. Vendors pay a fraction of what players will, so the real money means farming stock first, then listing it on the Exchange and waiting for it to sell.
Why buy it
Solari belongs to your character, ready for the next schematic, vehicle module or Exchange buy without a night of chest runs first. Chapter 3 removed base taxes, so there's no weekly bill eating into it once it's banked.