Fortunately if you are a software developer, you can make things that other people require a lot of capital to do. So you can make your software vending machine of some sort and have passive income from that. Advertising it requires capital, and you have to design the system that has low infrastructure costs.
If there was a magic way to make money without work, everyone would be doing it.
1. find a profitable niche
2. solve a problem for that niche
3. do marketing in that niche to get people to pay for what you've done
In practice, making a passive income is tough and it's way easier and faster to be working for someone else. If 0.1% of my users would be customer I would be doing much better than my day job, until then I'm in the marathon of bootstrapping my business. Good luck!
1. Businesses I founded & own that are managed & operated by my employees. 2. REITs & other dividend paying stocks. 3. Real property that I own that is managed by property managers. 4. Music that I have published and receive streaming royalties on. 5. Personal loans (this is risky and I don't recommend it, but I do make some passive income this way). 6. Crypto lending (I use Stablegains which is currently paying 15%(!). Use my referral code to get $25 FREE when you sign up: https://app.stablegains.com/signup?ref=SWKDN4UXUG 7. Asset trade-ups to capture capital gains (such as in real estate). 8. Leveraging credit card cash back rewards by using these types of cards for ALL of my purchases, business and personal.
These are my primary income earners, and when added together, they make quite a sum of passive income for me. I started at zero like many of you here. It is possible to build a diverse portfolio of passive income with relatively low risk, without starting with a ton of capital. It just takes some good ideas, excellent execution of those ideas, self-control over your spending, and smart decision making. Don't lease the new Tesla when you can get by with the $5k SUV you already own. Those kind of things.
"Passive income" as it's sold to people on social media frankly doesn't exist. You work hard, build something other people want, and people pay you for it.
1) Save some money regularly (min 10%). 2) If 1) seems difficult, figure out a way to increase your earnings or reduce your expenses till you can do 1). 3) Invest the surplus wisely. Trust it to people who are trustworthy and seem to know their stuff.
Overtime, you will have enough passive income.
If you want passive income without any type of upfront work, you might look into renting stuff out that you possess. House? Why not rent a part to someone? A car, or other tools? Maybe you can rent them to somebody.
Once you secure "normal" income, save up in Bitcoin. This will at the very least protect your purchasing power against inflation. With a little bit of luck your purchasing power will grow as Bitcoin gets adopted.
The key is to find something you can create once and sell multiple times.
Be prepared for the amount of time you’ll have to spend to start making “passive” income
So, you'll have to maximize income and reduce cost as much as possible to fill that "investment bag". One way to do that is to become self-employed, win a corporate customer that is okay with remote work and move to a lower-income / cost country for 10 years.
A lot of people today try to build traction for their digital product in a large enough niche. Never ever underestimate the effort needed for that! That hasn't much to do with passive income.
If you've got a talent for writing, you could write 9.99€ Kindle books for high margins.
You're in Berlin. Why not have some tutoring business specifically to Berliners? Then after you've done some tutoring, anticipate whatever next-level skill they need and upsell those online courses.
Just brainstorming
Save up to buy a home. Then save up to buy a second one. Rent out the second one while paying someone to manage it for you. Rinse and repeat.
Maybe try feudalism, though.