It's not easy to find students when you just start, coz online teaching is a new stream and needs a certain level of trust as well...
You can place add on Gumtree or smth like that and just trust your students (they usually dont prepay for lessons).
To make sure you'll be paid for your time you'd better work through online language schools, but sometimes they ask too much information and skills\certificates confirmations, which makes process longer. Also, they'll make sure you have everything to provide good quality service - good internet connection, headphones and microphone,you should be online 2-4 hours every day. After registration you'll have to wait new students who'll pick you up among all other teachers before getting started. And, by the way, a lot of online schools offer at least one free lesson to get started. But in this case you know you'll get your money,after school get it's part though
Or you can use StretchPay, in this case there is no third part involved. You and your students must have PayPal account and that's it. The amount of money you get will only depend on your professional qualities and relationships between you and your student.