Layer7 API Management

I am getting a JSON from CA LAC. In that JSON I have to increment the value of a variable and then send the update to the backend. SO how can I perform an increment operation on a variable?

I tried the following approach but it's not working,

* Extract variable from JSON using Evaluate JSON Path Expression Assertion

* Then setting one context variable having value 1

* Then setting another context variable with the expression :

         ${variable1.result} + ${variable2}

But it's not working.

set context variable assertion will not do calculating.

you can use xpath assertion to do calculating.

I will attach an example policy

Thanks!!