Unresolved reference on org.gradle.api dependencies after migrating build.gradle file to build.gradle.kts in buildSrc directory

I am trying to migrate my build.gradle file to build.gradle.kts in my buildSrc directory. Note that in my buildSrc I already create a gradle plugin using java-gradle-plugin and using api from org.gradle.api such as Plugin, Project etc. But when I configured the script I got an unresolved reference inside my file whom using org.gradle.api

here is the code for the build.gradle file

plugins {
    id 'java'
    id 'java-gradle-plugin'
    id 'org.jetbrains.kotlin.jvm' version '1.3.21'
}

gradlePlugin {
    plugins {
        netguard {
            id = 'pluginId'
            implementationClass = 'myplugin.plugin.awesomeplugin'
        }
    }
}
repositories {
    mavenCentral()
}
dependencies {
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8"
}
compileKotlin {
    kotlinOptions {
        jvmTarget = "1.8"
    }
}
compileTestKotlin {
    kotlinOptions {
        jvmTarget = "1.8"
    }
}

and this is the migrated build.gradle.kts

import org.gradle.kotlin.dsl.*
import org.jetbrains.kotlin.gradle.tasks.KotlinCompile


plugins {
    `kotlin-dsl`
    java
    `java-gradle-plugin`
    id("org.jetbrains.kotlin.jvm") version "1.3.21"

}

gradlePlugin {
    plugins {
        create("netguard") {
            id = "pluginId"
            implementationClass = "myplugin.plugin.awesomeplugin"
        }
    }
}

repositories {
    mavenCentral()
}

dependencies {
    implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8")
}

val compileKotlin: KotlinCompile by tasks
compileKotlin.kotlinOptions.jvmTarget = "1.8"

val compileTestKotlin: KotlinCompile by tasks
compileTestKotlin.kotlinOptions.jvmTarget = "1.8"

here some unresolved reference from org.gradle.api

org.gradle.api.Plugin
org.gradle.api.Project
org.gradle.api.file.ConfigurableFileTree
org.gradle.testing.jacoco.plugins.JacocoPluginExtension
org.gradle.testing.jacoco.tasks.JacocoCoverageVerification
org.gradle.testing.jacoco.tasks.JacocoReport
...

any help will be very much appreciated. thank you!