Why I can’t buy something by smartpay on my iPad?

Hello veasna293,

I would appear you are having an issue purchasing from the App Store. Here is some information we hope will help.

Start by looking over the payment methods that are accepted in your region: Payment methods that you can use with your Apple ID - Apple Support

If the payment you are looking to use is listed, and you continue to have an issue, please provide any messages that may appear exactly as they are worded. This will assist others here to provide the best solution possible.

Have a great day.