Do I need special training to do online therapy?

Yes, in my opinion, you do. There are security issues, ethical issues, and legal issues that you may just not think of on your own. There are also many tips and tricks to doing great work online that make a big impact on the effectiveness of your therapy. Some states require that you take a certain number of CEUS in telehealth, or complete a certification. Some do not. Some insurance companies will require the same. Some do not. Some professional ethics require the same. Some do not. But good practice? Ensure your competence to treat clients via a mode that is new to you.