i buy one app but that is not proper work and some function not working?

[iMore Question]

and now i want refund

 

[BlackNightmare]

To ask for a refund, you just have to head to the dedicated Apple address: http://reportaproblem.apple.com/
Once logged in, you can select which purchase gives you problem and select the cause for the report (faulty app, not authorized access, and so on). Here's the official Apple guide for the procedure: https://support.apple.com/en-us/HT204084