Toptal: Didn't hear it before.

Turing: I took their test (C#, 40 questions if not mistaken) and passed, but never had the gut to solve their coding challenge online. (Turing is hiring remote workers to work with companies in Silicon Valley)

Freelancer.com: Didn't succeed except their online contest:

Examples:


I helped inventing a new name and won EUR 4.50 (too little, I know). Also earned USD 1 for giving consultation to a person from South Asia.
Freelancer.com needs membership fee (or else it is very limited), what I earned not even enough to pay for it.

Upwork: Succeeded in creating a profile, but I deleted my account afterward.
(It is very difficult, from what I heard, to have our profiles approved)

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Don't give up, TS, keep trying.

TS, did you try Fiverr, selling your skill on that platform is easy, no membership whatsoever. I posted one yesterday. You can choose web / mobile /desktop development, it even let you to categorize your pricing, like Basic, Standard ,Premium (can't remember the exact phrase).