OPPO/Realme Android 9.x Guide

These Settings must be properly configured to keep Mobile Tracker Free working.

Info: A password may be required to access the application settings. If you have not changed, the default password is *1234*. More information about the application password here.

• Settings => Dual SIM & Cellular Network => Using Wi-Fi and Cellular Network => « Wi-Fi » => Select 'Wi-Fi and Mobile data'
• Settings => Dual SIM & Cellular Network => Data Saving => Turn OFF
• Settings => Security => Permissions => Apps => « Wi-Fi » => Allow All
• Settings => Battery => Power Saving Mode => Turn OFF
• Settings => Battery => Smart Power Saver => Turn OFF
• Settings => Battery => Power saver options => Sleep Standby Optimization => Turn OFF
• Settings => App Management => « Wi-Fi » => Data Usage Status => Network Permissions => Wi-Fi and Mobile Data
• Settings => App Management => « Wi-Fi » => Data Usage Status => Background data => Turn ON
• Settings => App Management => « Wi-Fi » => Data Usage Status => Unrestricted by "Data Saving" => Turn ON
• Settings => App Management => « Wi-Fi » => Power Saver => Allow Background Running => Turn ON
• Settings => App Management => « Wi-Fi » => Permissions => Allow All
• Settings => App Management => « Wi-Fi » => Auto Startup => Turn ON
• Settings => App Management => « Wi-Fi » => Floating Windows => Turn ON
• Settings => Device & Privacy => Location => Apps Using GPS in Background => « Wi-Fi » => Turn ON

Be careful, with ColorOS 6 :

• During an audio recording, the notification bar will blink red to warn you that a recording is in progress.

It is not possible to hide this, it is a security of the ColosOS system.