Could not find manifest-merger.jar (com.android.tools.build:manifest-merger:26.0.0) in ionic3?

This solution worked for me

1- In the CordovaLib folder and in the build.gradle file, change the position of the Maven up

Repositories {
   maven {
         url "https://maven.google.com"
   }
   jcenter()
}

2- In the general build.gradle file of the project change the position of Maven up and add google()

Repositories {
   maven {
         url "https://maven.google.com"
   }
   google()
   jcenter()
}

3- In the build.gradle file of the APP folder change the position of Maven up and add google()

buildscript {
    repositories {
        maven {
            url "https://maven.google.com"
        }
        google()
        mavenCentral()
        jcenter()

    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.0.0'
    }
}

// Allow plugins to declare Maven dependencies via build-extras.gradle.
allprojects {
    repositories {
        google()
        mavenCentral();
        jcenter()
    }
}

4 - Finally, run the "Make Project" that is in the upper corner of Android Studio.

I did the following :

ionic cordova platform remove android ionic cordova platform add android ionic build android

And it worked!