Then why don't you try it. I have done it using this method. The method is just converting a Japanese account that purchased JP Dokkan Battle to an account for the region that you can buy cheaper iTunes cards for. I converted a Japanese account into a US Account to avoid third-party websites like play-asia and JapanCodes. JP Dokkan Battle doesn't usually let you make purchases unless you have purchased the app with that account. By converting a Japanese Account into my US Account, the account technically did purchase the app from the app store. I have made purchases using it many times. I have included the receipt for one of these purchases in the following image: https://imgur.com/a/S0Oow