Jenkinsfile Pipeline errors: “expected a step” and “undefined section”

Can anyone explain why I get the following errors, and what can be a possible solution for them?

Running in Durability level: MAX_SURVIVABILITY
org.codehaus.groovy.control.MultipleCompilationErrorsException:
startup failed: WorkflowScript: 43: Expected a step @ line 43, column
17.
if (isUnix()) {
^

WorkflowScript: 71: Undefined section "success" @ line 71, column 5.
success {
^

WorkflowScript: 78: Undefined section "failure" @ line 78, column 5.
failure {
^

WorkflowScript: 16: Tool type "maven" does not have an install of
"MAVEN_HOME" configured – did you mean "Maven M2"? @ line 16, column
19.
maven "MAVEN_HOME"
^

WorkflowScript: 17: Tool type "jdk" does not have an install of
"JAVA_HOME" configured – did you mean "null"? @ line 17, column 17.
jdk "JAVA_HOME"
^

The code in the Jenkinsfile is as follows:

  pipeline {

        // agent defines where the pipeline will run.
        agent {
            // Here we define that we wish to run on the agent with the label SL202_win
            label "SL202_win"
        }

        // The tools directive allows you to automatically install tools configured in
        // Jenkins - note that it doesn't work inside Docker containers currently.
        tools {
            // Here we have pairs of tool symbols (not all tools have symbols, so if you
            // try to use one from a plugin you've got installed and get an error and the
            // tool isn't listed in the possible values, open a JIRA against that tool!)
            // and installations configured in your Jenkins master's tools configuration.
            maven "MAVEN_HOME"
            jdk "JAVA_HOME"
        }

        environment {
            // Environment variable identifiers need to be both valid bash variable
            // identifiers and valid Groovy variable identifiers. If you use an invalid
            // identifier, you'll get an error at validation time.
            // Right now, you can't do more complicated Groovy expressions or nesting of
            // other env vars in environment variable values, but that will be possible
            // when https://issues.jenkins-ci.org/browse/JENKINS-41748 is merged and
            // released.
            mvnHome = "D:/Tools/apache-maven-3.5.2"
        }

        stages {
            // At least one stage is required.
            stage("Preparation") {
                // Every stage must have a steps block containing at least one step.
                steps {
                    // Get some code from a GitHub repository
                    git 'https://git.ceesiesdomain.nl/scm/rsd/test_automation.git'
                }
            }
            stage('Build') {
                steps {
                // Run the maven build
                if (isUnix()) {
                    sh "'${mvnHome}/bin/mvn' clean test -Dtest=TestRunner"
                } else {
                    bat(/"${mvnHome}\bin\mvn" clean test -Dtest=TestRunner/)
                }
            }
        }
            stage('Results') {
            steps {
                cucumber buildStatus: 'UNSTABLE', failedFeaturesNumber: 999, failedScenariosNumber: 999, failedStepsNumber: 3, fileIncludePattern: '**/*.json', skippedStepsNumber: 999
            }
        }
    }
        // Post can be used both on individual stages and for the entire build.
        post {
            success {
                echo "Test run completed succesfully."
            }
            failure {
                echo "Test run failed."
            }
            always {
        // Let's wipe out the workspace before we finish!
                deleteDir()
                echo "Workspace cleaned"
            }
    }

    success {
        mail(from: "jenkins@ceesiesdomain.nl",
                to: "ceesie@ceesiesdomain.nl",
                subject: "That build passed.",
                body: "Nothing to see here")
    }

    failure {
        mail(from: "jenkins@ceesiesdomain.nl",
                to: "ceesie@ceesiesdomain.nl",
                subject: "That build failed!",
                body: "Nothing to see here")
    }

    // The options directive is for configuration that applies to the whole job.
    options {
        // For example, we'd like to make sure we only keep 10 builds at a time, so
        // we don't fill up our storage!
        buildDiscarder(logRotator(numToKeepStr:'10'))

        // And we'd really like to be sure that this build doesn't hang forever, so
        // let's time it out after an hour.
        timeout(time: 60, unit: 'MINUTES')
    }
}