Android operating systems

Android version 6.0.1+

Verify that the battery optimization is not preventing Rainbow from sending you notifications:

From the application drawer, open Settings.
Select Battery.
Open the Overflow menu icon  and choose Battery Optimization.
Tap the downward caret and choose All apps.
Search and select Rainbow, then tap Don't optimize.

Android version 7+

From the application drawer, open Settings.
Select Apps.
Find and select Rainbow.
Select Battery, then open Battery Optimization.
At this point, select Apps not optimized option and modify it to All apps.
Search and select Rainbow and set to Don't optimize.

Android version 9

Verify that the the Adaptive Battery feature is not preventing Rainbow from sending you notifications:

From the application drawer, open Settings.
Select Battery.
Choose Adaptive Battery.
Select Restricted apps, and make sure Rainbow is not listed here.

OPPO

On OPPO devices you have to check different settings:

Setting 1: Verify that Rainbow is a protected application

From the application drawer, open Settings.
Select Advanced Settings.
Select Battery Manager, then open Protected Apps.
Select Rainbow to enable protection.

Setting 2: Verify that Rainbow is exclude from battery optimization

Open Settings.
Select Battery, then select Energy Saver.
Search Rainbow and verify that Freeze when in Background, Abnormal Apps Optimization and Doze are all disabled.

Setting 3: Verify that notifications are allowed for Rainbow

From the application drawer, open Settings.
Open Notification Panel & Status Bar.
Open Notification Center.
Activate allow notifications and priority display for Rainbow.

Setting 4: Verify that Rainbow is in the start up manager

Open the Security application.
Open Privacy Permissions, then Start up manager.
Ensure that this setting is enabled for Rainbow.

XIAOMI

On Xiaomi devices you have to check different settings:

Setting 1: Verify that Rainbow is allowed to autostart

From the application drawer, open Security.
Select Permissions.
Select Autostart.
Ensure that this setting is enabled for Rainbow.

Setting 2: Verify that Rainbow has no battery restriction

Open Settings.
Select Battery, then select Energy Saver.
Search Rainbow and verify that Freeze when in Background, Abnormal Apps Optimization and Doze are all disabled.

Setting 3: Verify that notifications are allowed for Rainbow

From the application drawer, open Settings.
Open Notification Panel & Status Bar.
Open Notification Center.
Activate allow notifications and priority display for Rainbow.

Setting 4: Verify that Rainbow is locked in the "recent applications" / "application overview" plane.

Open the application drawer, then select "recent apps/overview button"
Find Rainbow,pull down on it to "lock it"