Camunda Rest API with XML Content

Hi, can i start a process over the REST Api with a XML body?
And if yes, how?

Example:
Send tin the request body to the process instance start endpoint:
http://localhost:8080/rest/process-definition/key/{your process definition id}/start

{
    "variables": {
        "REQUESTJSON": {
            "value":"<cal:CalculateNetAmountResponse xmlns:cal=\"http://www.celfocus.com/CalculateNetAmount\"><cal:field>stringField</cal:field><cal:error>stringError</cal:error></cal:CalculateNetAmountResponse>",
            "type": "xml"
        }
    },
    "businessKey": "myBusinessKey",
    "withVariablesInReturn" : "true"
}