If you want to assert it with the response, add script assertion and paste below assertion
import groovy.json.*
def jsonText = messageExchange.response.responseContent
def jsonSlurper = new JsonSlurper()
def object = jsonSlurper.parseText(jsonText)
object.InventoryAvailability.each{element ->
log.info element.availableQuantity+":"+element.inventoryStatus
if (1 <= Float.parseFloat(element.availableQuantity)) {
assert element.inventoryStatus == "Available" : "Incorrect available status when quantity greater than 1"
} else {
assert element.inventoryStatus == "Unavailable" : "Incorrect available status when quantity less than 1"
}
}