Solved, I had to fix my RetrofitInstance class to include JSON parsing

object RetrofitInstance {

    fun getInstance(): WeatherAPI {
        val retrofit = Retrofit.Builder()
            .baseUrl(BASE_URL)
            .apply {
                    addConverterFactory(
                        Json { ignoreUnknownKeys = true }
                            .asConverterFactory("application/json".toMediaType())
                    )
            }
            .build()

        return retrofit.create(WeatherAPI::class.java)
    }
}