Don't mind reading my answer if you have a relatively high paying job.
Tried a few online methods over the course of years. Failed at most. Learnt from plenty.
Two that gave me most revenue/time were
* Teaming up with a few friends and completing projects for undergrad students. I was stunned to find out most were willing to pay 15k-20k(group projects assigned to 3-4 students) for a simple project as long as you document it well enough for them to be able to understand and fake it as their own. No dearth of students who just want to chill out in their final year after placements.
* Grew a meme page organically to 25K. Got traction on merchandise sells through FB ads. Reach died eventually and page went stale
Having said all this, I have a different take. And it's backed by my own research. YMMV.
I like to stay connected with people who have 'made it' in life. Sort of like a casual mentor/mentee thing. While there is no formula to success, patterns do emerge. They have learnt this the hard way. It only makes sense that you learn and adapt. Based on my incessant conversations with such folks, I observed that the most efficient way to increase your earnings will be to get a massive pay raise. As early in your career as possible. Don't stay at one company for more than 2-3 years. Jump ships quick and raise that TC!
If you're ready to sacrifice 6-8 months of your time after work, you might end up with 1.5X the pay cheque.(I'm at this junction of life right now)
There are reasons to do this. Most critical ones being super high leverage of money and network of connections. Once you have spent 4-5 years perfecting your domain expertise without letting online 'side-hustles' fragment your focus, you are way ahead of your colleague curve.
* A hefty bank balance gives you so many options. You can dip your feet in plenty of ventures. Stocks, Miniature startup angel investing, Buying out small SAAS, Any creative agencies, Realtor.. The world is your oyster. Having a cushion of 'F@#k you!' and 'F@#k it!' money will give you a chance to try so so many things and plus do it for premium, just because your word now has value as an established someone. Most importantly, you'll have a substantial amount that you won't mind to just forego if things don't work out. The 'F#$k it' money.
* You build undeniable credibility - big name companies help immensely with this. Exposure to the smartest people will compound your chances of finding successful unicorns before it's too late. I can't stress this enough. We tend be lone asocial warriors as coders. But knowing the right people will increase your odds of being 'really' successful multifolds..Develop connections early on.. You'll need to know them before you'll need them..
TLDR: Not the direct answer. Quite tangential. If not there already, work hard on getting into a steadily high-paying job as early as possible. Not minding low work-life balance for 7-8 years early on will reap enormous rewards later. Then get into earning online or any other avenue you might want to pursue. Might seem unthinkable/unfeasible at the moment, but your odds will have significantly improved. Many people with limited smarts have done it before. You should definitely be unique and pave your own path. But it would suck to not realize what has worked for many. Study them.
That ended up being way too philosophical and verbose.
Thanks for coming to my Ted talk. This kind of topic is near and dear to me. I can go on and on but will cautiously choose to end this train of thought here. It's Friday after all..