gradle swagger plugin DSL is not recognised in build.gradle.kts

Hi,
I'm trying using the gradle plugin

id("io.swagger.core.v3.swagger-gradle-plugin") version "2.1.5"

When adding the following DSL as in the git README, it is not recognised by gradle 
The project is a Kotlin project with Spring Boot + SpringFox
Tx

resolve {
    outputFileName = 'PetStoreAPI'
    outputFormat = 'JSON'
    prettyPrint = 'TRUE'
    classpath = sourceSets.main.runtimeClasspath
    resourcePackages = ['io.test']
    outputDir = file('test')
}