Installed xamarin android .apk file only work for 24 hours

Hello, I am using paid version of xamarin studio for android application. Whenever I am installing my.apk file , I am getting message " Build with evaluation software This build will only work for 24 hours." After 24 hours my installed application .apk file has not been worked for us. So please provide me the relevant solution for this problem

Thanks 

Sanjaya Verma