Gold is the most valuable resource in Crusader Kings 3. You can buy entire armies and persuade anyone to like you with enough money. Gold is not supposed to be easy or fast to get, but there is a way around that.
Golden Obligations is a perk you should have in every game because it makes getting gold easy and fast. Navigate to Lifestyles at the bottom left of your screen, then pick Stewardship and focus your character on Avaricious. The first perk in this focus is Golden Obligations.
This perk enables you to sell the Hooks you have on anyone in Crusader Kings 3, as long as the person is within your diplomatic range. Family, friends, and enemies' Hooks can be sold for up to 300 Gold.
How to get a Hook on someone
Selling Hooks is basically extortion through blackmail, which is the technical term for buying silence. To sell Hooks, you have to get Hooks first. You can earn Hooks through random events, but the best way is to send your Spymaster on a mission to discover secrets in another country.
To send your Spymaster to do your bidding, go to Council and select the find secrets option at the bottom of your Spymaster's tab. You can then assign your Spymaster to uncover secrets in any council worldwide, though you may want to stick close to home to maximize efficiency. After the Spymaster has found something on a character, you can blackmail them by right-clicking on their character portrait and selecting Blackmail. It's more likely that they will accept a Hook if it's a bigger or darker secret.
When you have a Hook on someone, you can right-click their portrait and choose Demand Payment. This will only work if the character has enough money to pay off their Hooks. If not, you cannot require payment. In the event that you have a strong Hook, you can continuously demand payments, one after another, over time. When you have a weak Hook, you will only be able to grab money once. It's like getting dividends from your blackmail investments if you do this enough.
For more on Crusader Kings 3, check out What is the best Duchy building in Crusader Kings 3? or What is Cultural Acceptance in Crusader Kings 3: Royal Court and how to increase it here on Pro Game Guides!