Stuck with Unresolved reference: ksp error in Android Gradle

I have started building a simple android app. But I am stuck with Unresolved reference: ksp error. I am managing all plugin versions in libs.versions.toml. Below are gradle files and libs file. Can anyone help me what's wrong with my code?

libs.versions.toml

[versions]
agp = "8.1.0"
kotlin = "1.9.0"
core-ktx = "1.10.1"
appcompat = "1.6.1"
material = "1.9.0"
constraintlayout = "2.1.4"
coroutines = "1.7.3"
lifecycle = "2.6.1"
room = "2.5.2"
recyclerview = "1.3.1"
datastore-preferences = "1.0.0"

# Testing libraries
junit = "4.13.2"
androidx-junit = "1.1.5"
espresso-core = "3.5.1"

# SDK versions
minSdk = 24
compileSdk = 34
targetSdk = 34

ksp = "1.9.0-1.0.12" # Add KSP version

[libraries]
core-ktx = { group = "androidx.core", name = "core-ktx", version.ref = "core-ktx" }
appcompat = { group = "androidx.appcompat", name = "appcompat", version.ref = "appcompat" }
material = { group = "com.google.android.material", name = "material", version.ref = "material" }
constraintlayout = { group = "androidx.constraintlayout", name = "constraintlayout", version.ref = "constraintlayout" }
coroutines-android = { group = "org.jetbrains.kotlinx", name = "kotlinx-coroutines-android", version.ref = "coroutines" }
lifecycle-viewmodel-ktx = { group = "androidx.lifecycle", name = "lifecycle-viewmodel-ktx", version.ref = "lifecycle" }
lifecycle-runtime-ktx = { group = "androidx.lifecycle", name = "lifecycle-runtime-ktx", version.ref = "lifecycle" }
room-runtime = { group = "androidx.room", name = "room-runtime", version.ref = "room" }
room-ktx = { group = "androidx.room", name = "room-ktx", version.ref = "room" }
room-compiler = { group = "androidx.room", name = "room-compiler", version.ref = "room" }
recyclerview = { group = "androidx.recyclerview", name = "recyclerview", version.ref = "recyclerview" }
datastore-preferences = { group = "androidx.datastore", name = "datastore-preferences", version.ref = "datastore-preferences" }

# Testing libraries
junit = { group = "junit", name = "junit", version.ref = "junit" }
androidx-junit = { group = "androidx.test.ext", name = "junit", version.ref = "androidx-junit" }
espresso-core = { group = "androidx.test.espresso", name = "espresso-core", version.ref = "espresso-core" }

[plugins]
androidApplication = { id = "com.android.application", version.ref = "agp" }
androidLibrary = { id = "com.android.library", version.ref = "agp" }
kotlinAndroid = { id = "org.jetbrains.kotlin.android", version.ref = "kotlin" }
kotlin-ksp = { id = "com.google.devtools.ksp", version.ref = "ksp" }

Settings.gradle.kts

pluginManagement {
    repositories {
        google()
        mavenCentral()
        gradlePluginPortal()
    }
}
dependencyResolutionManagement {
    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
    repositories {
        google()
        mavenCentral()
    }
    versionCatalogs {
        create("libs") {
            from(files("gradle/libs.versions.toml"))
        }
    }
}
rootProject.name = "Naturo"
include(":app")

build.gradle.kts (Project)

// Top-level build file where you can add configuration options common to all sub-projects/modules.
plugins {
    alias(libs.plugins.androidApplication) apply false // Apply Android Application plugin
    alias(libs.plugins.androidLibrary) apply false // Apply Android Library plugin
    alias(libs.plugins.kotlinAndroid) apply false // Apply Kotlin Android plugin
}

build.gradle.kts (Module :app)

plugins {
    id("com.android.application")
    id("org.jetbrains.kotlin.android")
    id("androidx.navigation.safeargs.kotlin") // Add Safe Args plugin if using Navigation
    id("com.google.devtools.ksp") // Use KSP for Room annotation processing
}

android {
    namespace = "com.minimalapps.naturo"
    compileSdk = libs.versions.compileSdk.get().toInt()

    defaultConfig {
        applicationId = "com.minimalapps.naturo"
        minSdk = libs.versions.minSdk.get().toInt()
        targetSdk = libs.versions.targetSdk.get().toInt()
        versionCode = 1
        versionName = "1.0"

        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            isMinifyEnabled = true
            proguardFiles(
                getDefaultProguardFile("proguard-android-optimize.txt"),
                "proguard-rules.pro"
            )
        }
    }
    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_1_8
        targetCompatibility = JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = "1.8"
    }
    buildFeatures {
        viewBinding = true
    }
}

dependencies {

    implementation(libs.core.ktx)
    implementation(libs.appcompat)
    implementation(libs.material)
    implementation(libs.constraintlayout)
    implementation(libs.recyclerview)
    implementation(libs.lifecycle.viewmodel.ktx)
    implementation(libs.lifecycle.runtime.ktx)
    implementation(libs.coroutines.android)
    implementation(libs.room.runtime)
    implementation(libs.room.ktx)
    ksp(libs.room.compiler) // Use ksp instead of kapt
    implementation(libs.datastore.preferences)

    testImplementation(libs.junit)
    androidTestImplementation(libs.androidx.junit)
    androidTestImplementation(libs.espresso.core)
}

Help me fix this

Solution

You already apply the KSP plugin in your module, but you need to add it to your top-level build.gradle.kts first before it can be applied:

alias(libs.plugins.kotlin.ksp) apply false

As always you need to perform a gradle sync after changing the gradle setup before you can use it.

That said, when trying to use your gradle setup I also had to adjust the following to get it running:

Remove the following from your settings.gradle.kts. Gradle will automatically search for the version catalog at that location:
```
versionCatalogs {
    create("libs") {
        from(files("gradle/libs.versions.toml"))
    }
}
```
In the version catalog versions must be delcare as String, not as a number:
```
minSdk = "24"
compileSdk = "34"
targetSdk = "34"
```
Remove the Safe Args plugin from the module level build.gradle.kts:
```
id("androidx.navigation.safeargs.kotlin") // Add Safe Args plugin if using 
```
It isn't needed since you do not use the navigation library in the first place. If you want to add it at a later time please see here how to properly set it up: https://developer.android.com/guide/navigation/use-graph/safe-args#kts