Unresolved reference for gradle dependency - kotlin

Question

All the classes of the library are shown in the libs folder but when I try to use any reference to it, it just says it is an unresolved reference.
Unresolved reference error
build.gradle.kts:
plugins {
kotlin("jvm") version "1.8.0"
kotlin("plugin.serialization") version "1.8.0"
id("com.github.johnrengelman.shadow") version "7.1.2"
id("io.papermc.paperweight.userdev") version "1.3.6"
}
group = "me.supehsloht"
version = "1.0-SNAPSHOT"
repositories {
mavenCentral()
maven("https://repo.rapture.pw/repository/maven-snapshots/")
}
dependencies {
compileOnly("org.jetbrains.kotlin:kotlin-stdlib:1.8.0")
compileOnly("org.jetbrains.kotlinx:kotlinx-serialization-json:1.4.1")
compileOnly("com.charleskorn.kaml:kaml:0.49.0")
paperDevBundle("1.19.3-R0.1-SNAPSHOT")
compileOnly(files("libs/Core.jar"))
compileOnly(files("libs/AdvancedSlimeWorldManagerAPI.jar"))
}
java {
toolchain.languageVersion.set(JavaLanguageVersion.of(17))
}
tasks {
compileJava {
options.encoding = Charsets.UTF_8.name()
options.release.set(17)
}
compileKotlin {
kotlinOptions.jvmTarget = "17"
}
reobfJar {
outputJar.set(layout.buildDirectory.file("libs/${project.name.capitalize()}.jar"))
}
}
I already had this problem, then it was fixed by not shading the kotlin stdlib into the jar but that didn't work this time.