Why can't kotest be found?

Question

According to every guide there is, in order to use kotest in IntelliJ for a Kotlin project using gradle, I need to add this to my build.gradle.kts:

plugins {
    .
    .
    .
    id("io.kotest") version "5.8.0"
}

And this repository information should be sufficient

repositories {
    mavenLocal()
    mavenCentral()
}

Yet, ./gradlew clean fails with:

FAILURE: Build failed with an exception.

* Where:
Build file '{path}/build.gradle.kts' line: 1

* What went wrong:
Plugin [id: 'io.kotest', version: '5.8.0'] was not found in any of the following sources:

- Gradle Core Plugins (plugin is not in 'org.gradle' namespace)
- Plugin Repositories (could not resolve plugin artifact 'io.kotest:io.kotest.gradle.plugin:5.8.0')
  Searched in the following repositories:
    Gradle Central Plugin Repository