An online qualification will be enough to find you work, particularly across Asia.

You'll find that some schools prefer qualifications such as tesol or celta which include observed teaching time. These courses are more expensive but I'd recommend taking one if you plan to teach esl for a few years or more as they will open up further job opportunities and can help you command a higher wage. However, if you are just thinking about spending a year or so teaching then an online certificate is good choice.

My guess is that you're not a native English speaker (apologies if I'm wrong). This, along with experience and qualifications will also play an important part in determining which jobs are available to you. You can't change the fact you're a non-native speaker but you can always gain further professional qualifications.