Hi there,
To extract “selenium_test_id” from REST call #1 (response variable in my case)
def slurper = new groovy.json.JsonSlurper()
def result = slurper.parseText(response.getResponseBodyContent())
println result.selenium_id
2. Add to REST Call #2 (request in my case)
request = request.setRestUrl("https://crossbrowsertesting.com/api/v3/selenium/" + result.selenium_id)
Hope it help you in this case