Many people do this, and most freelance platforms do not ask about your employment status when you sign up. The platform itself usually has no rule against it. However, your full-time job contract might have a clause that restricts you from doing outside work, especially in the same field. So the restriction, if any, comes from your employer and not the freelance platform. It is always better to read your employment agreement before you start taking freelance work. Has anyone here dealt with this situation before?