I would strongly suggest to you to get a certification that is not online. Kettlebells are very versatile and knowing the correct movements and technique are crucial when teaching them to others. Although there are different certifications out there, I would suggest RKC because of the level of instructors, support and instruction quality. Even though it’s on the high end of pricing, your money will be well spent. Again, this is only a suggestion.
I’m with Harris on this one.
Do you have experience swinging kettlebells, supervised by a certified instructor so that you know your foundation skills are solid? Kettlebells have wonderful properties, but proper form is the difference between power and injury. It takes a lot of practice, and before teaching anyone else how to swing, I would think you’d want to have your own form critically examined, which can’t be done online.