What Facebook used is not the default password and alias for debug. You need to change it following and it will work.
/usr/lib/jvm/jdk1.8.0_66/bin/keytool -exportcert -alias androiddebugkey -keystore ~/.android/debug.keystore | openssl sha1 -binary | openssl base64
If you have not changed anything with the default password it should be "android".
You can also configure it in the build.gradle file. But the same alias password should be used for generating the hash:
android {
signingConfigs {
release {
storeFile file("~/.android/debug.keystore")
storePassword "android"
keyAlias "androiddebugkey"
keyPassword "android"
}
}
}