wso2 – Converting json to soap+xml to send to endpoint

I converted this json file to XML
{ "firstNumber": 25, "secondNumber": 23 }

but it converts it to this instead;
<Add xmlns="http://tempuri.org/"> <a>25</a> <b>23</b> </Add>

Now, without headers for soap and the envelop, the endpoint does not recognize this so i use an enrich mediator to make it the right format.

the issue i have is that when i use the enrich mediator, it replaces the entire soap body including the variables.

is there a way i can change only the envelop of the xml message

this is my endpoint
ecs.syr.edu/faculty/fawcett/Handouts/cse775/code/calcWebService/Calc.asmx
the documentation is there too

This is my code
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