If you're using Unity 2018.3+, you can setup notifications throught built-in Unity package https://docs.unity3d.com/Packages/com.unity.mobile.notifications@1.0/manual/index.html

Unity3D Android notification plugin

License: MIT

Features:

• Set delayed notification
• Set delayed repeatable notification
• Supports custom icon and large icon
• Fully supports Unity 4.x, 5.x, 2017.x
• Fully supports Android 4.0.3 - 8.0
• Fully supports iOS 8.0 - 11.0

FAQ

How to set up small icon ?

Use the Android Asset Studio notification icons generator (https://romannurik.github.io/AndroidAssetStudio/icons-notification.html) to prepare small icons pack and replace temporary icons named notify_icon_small.png with the new ones in \UnityProject\Assets\Plugins\Android\res\

How to set up big icon ?

Same as small icon, but use launcher icons generator (https://romannurik.github.io/AndroidAssetStudio/icons-launcher.html) Just put the result into drawable directories \UnityProject\Assets\Plugins\Android\res\ with name notify_icon_big.png. And in the SendNotification method set bigIcon to "notify_icon_big".

If you want to use app icon just set bigIcon = "app_icon".

How to use a custom sound ?

For Android, place an .mp3 or .ogg sound file under Assets/Plugins/Android/res/raw in your Unity project. For iOS, place a .wav, .caf or .aiff sound under Assets/StreamingAssets. Make sure your Unity script that creates the notification sets the sound parameter to true and the soundName parameter to the name of your sound file, without an extension.

How to handle notification actions ?

When you create your Action, pass in a component (Like NotificationTest) that's attached to a game object that's guaranteed to be on your stage when your app starts. Also make sure that component has a method named "OnAction", or customize the name of the HandlerMethod when you create your Action. Whatever the name, the method must accept a single string parameter, which is the identifier of the action that was chosen.

On iOS, if you have more than one kind of notification with actions, make sure you use a different channel value for each kind.

How to create repeating notifications on iOS ?

iOS only supports repeat intervals of a minute, hour, day, 2-5 days (for 'weekday'), week, month, quarter or year. Make sure your timeout is the correct number of milliseconds for one of those values, like 60 * 1000 for a minute.

How to recompile Android plugin ?

There is special gradle task called exportJar, just run it and grab plugin's jar in app/release/notification.jar

How to get rid of obsolete warnings like "OBSOLETE - Providing Android resources in Assets/Plugins/Android/res is deprecated, please move your resources to an Android Library. See "Building Plugins for Android" section of the Manual." ?

You can avoid this by recompiling plugin with icons (and optionally sounds) inside.

Screenshot