Hardcoded value is working fine but not the assigned value

Hi All ,

I am setting up a value using webmethod action through restapi into another thirdparty system.

one of the json value If we set Hardcoded (ex : Apple Iphone6s-32GB) it is assigning the value without any issue , we but I set the same value which is my model and title (set a variable using buildstring action) ,it is not working as expected . which I check the history of the variable it is giving the same value (Apple Iphone6s-32GB).

May I know how to solve this ?

Thanks