Unresolved reference: app in Android Dynamic Module

I have a problem and I am creating an Android Bundle app, but I do not create the activities in the Dynamic Modules, I just get this error:

Unresolved reference: app

This is the main app build.gradle code:

    android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "bundletest.hitcel.com.bundletest"
        minSdkVersion 17
        targetSdkVersion 28
        versionCode 1
        versionName "1.0.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    bundle {
        language {
            enableSplit = true
        }
        density {
            enableSplit = true
        }
        abi {
            enableSplit = true
        }
    }


    dynamicFeatures = [":Chat", ":Estadisticas"]


}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
    api "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
}

and this one of my dynamic module:

apply plugin: 'com.android.dynamic-feature'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'

android {
    compileSdkVersion 28



    defaultConfig {
        minSdkVersion 17
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"


    }


}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation project(':app')
}

But it still does not work, start it based on the following Google Developers tutorial

enter the description of the link here

Neither Clean project nor Build Project solve and all this remains in red in my ChatActivity.tk:

package bundletest.hitcel.com.chat

import android.support.v7.app.AppCompatActivity
import android.os.Bundle

class ChatActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_chat)
    }
}

This is the structure of my project:

I would appreciate any suggestion to solve it. Thanks in advance.