"Unresolved Reference: github", "Unresolved Reference: harrysoft" Android SDK

Question

I'm trying to implement some simple Bluetooth data transfer functions for a class project, but keep running into the issue of the Android SDK not recognizing some external libraries for no apparent reason.

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.widget.Toast
import com.afollestad.materialdialogs.MaterialDialog
import com.example.accentus_login.Retrofit.INodeJS
import com.example.accentus_login.Retrofit.RetrofitClient
import com.github.javiersantos.materialstyleddialogs.MaterialStyledDialog //< This one
import com.rengwuxian.materialedittext.MaterialEditText
import io.reactivex.Scheduler
import io.reactivex.android.schedulers.AndroidSchedulers
import io.reactivex.disposables.CompositeDisposable
import io.reactivex.schedulers.Schedulers
import io.reactivex.schedulers.Schedulers.io
import kotlinx.android.synthetic.main.activity_main.*
import com.harrysoft.androidbluetoothserial.BluetoothManager; //< This one
import com.harrysoft.androidbluetoothserial.BluetoothSerialDevice; //< This one

I have marked the libraries that it doesn't want to recognize above.

This is my Project Level build.gradle

// Top-level build file where you can add configuration options common to all sub-projects/modules.
buildscript {
    repositories {
        google()
        mavenCentral()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:7.0.4'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:1.5.31"
        classpath 'com.github.dcendents:android-maven-gradle-plugin:2.0'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

This is my Module Level build.gradle

task clean(type: Delete) {
    delete rootProject.buildDir
}


plugins {
    id 'com.android.application'
    id 'kotlin-android'
    id 'kotlin-android-extensions'
}

android {
    compileSdk 31

    defaultConfig {
        applicationId "com.example.myapplication"
        minSdk 21
        targetSdk 31
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }
}

dependencies {

    implementation 'androidx.core:core-ktx:1.7.0'
    implementation 'androidx.appcompat:appcompat:1.4.1'
    implementation 'com.google.android.material:material:1.5.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.1'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'

    //RxJava
    implementation 'io.reactivex.rxjava2:rxandroid:2.0.2'
    implementation("io.reactivex.rxjava2:rxjava:2.2.21")

    //Retrofit2
    implementation 'com.squareup.retrofit2:adapter-rxjava2:2.3.0'
    implementation 'com.squareup.retrofit2:converter-scalars:2.3.0'

    //Material Edit Text
    implementation 'com.rengwuxian.materialedittext:library:2.1.4'
    //Material Button
    implementation group: 'com.google.android.material', name: 'material', version: '1.6.0-alpha02'

    //Material Style Dialog
    implementation 'com.github.javiersantos:MaterialStyledDialogs:3.0.2'
    implementation 'com.afollestad.material-dialogs:core:3.3.0'

    //Material Progress Bar
    implementation 'me.zhanghai.android.materialprogressbar:library:1.6.1'

    implementation 'com.github.harry1453:android-bluetooth-serial:v1.1'

    // RxJava is also required.
    implementation 'io.reactivex.rxjava2:rxjava:2.2.21'
    implementation 'io.reactivex.rxjava2:rxandroid:2.0.2'


    }

I am not sure what exactly I am doing wrong to have those libraries to not be recognized in any capacity.