Go to Settings > App Management > Safe Lagoon > allow Auto Startup

Tap Power Saver and allow Background Running

On Oppo devices that have a Security Center (or a Phone Manager), open the Security Center app and go to Privacy Permissions > Startup manager > allow Safe Lagoon

On some Oppo devices (eg. R9, R11, and A37f) go to Settings > Battery > Others > Safe Lagoon and uncheck all settings

On some other devices, go to Settings > Battery > Energy Saver > find Safe Lagoon > turn off "Background Freeze" and "Abnormal Apps Optimization"

On some other devices, go to Settings > Battery and storage > Battery manager and turn off Smart power saving. Tap Power consumption details > Optimize for excessive power consumption and uncheck Safe Lagoon

Tap the Overview button to open a list of recently used apps > find Safe Lagoon > press and swipe down > tap the "lock" button