Json payload parametrization in Uipath

I have this json payload for post request :{“name”:“test”,“salary”:“123”,“age”:“23”}. I wanted to parameterize it. So I assign 1 variable to each like for nameto=test, salaryto=123, ageto= 23 and payload body will look like “{”“name”":""{nameto}"","“salary”":""{salaryto}"","“age”":""{ageto}""}". But when I run this POST request it is not able to fetch the variable value assign to it. I am using “Httprequest” activity. Could anyone please provide update on same.