What is it you would like to say? There's nothing wrong with your sentence gramatically, but it would come off as "Can I start to use your product by buying it?" ("Is it possible to initiate the process by means of purchase?")
If it's an online service, maybe something along the lines of "決済完了次第、すぐに利用できますか?" or "Can I start using it as soon as the payment is finalized?"
February 4, 2016 at 8:58am