CODE EXAMPLE FOR DART

* In pubspec.yaml the flutter.plugin.{androidPackage,iosPrefix,pluginClass} keys are deprecated. Instead use the flutter.plugin.platforms key introduced in Flutter 1.10.0

There is a typo in your pubspec.yaml. The correct keyword is "platforms", not "platform". So this should fix it:

flutter:
  plugin:
    platforms:
      ios:
        pluginClass: FlutterBlePeripheralPlugin
      android:
        package: dev.steenbakker.flutter_ble_peripheral
        pluginClass: FlutterBlePeripheralPlugin