How to slove the background downloading not working problem?

1. Go to your phone settings and look for Permissions, then tap on Autostart




"For Mi 4:
Go to Permissions (or Security) > Auto-start > Enable HappyMod"
2. Close battery optimization.
"For Mi 4i:
Go to Phone Settings:
Additional Settings
Battery
Manage apps battery usage
Choose apps > HappyMod
Custom and in Background Network, choose to stay connected."
"Alternative solution:
Phone settings
Permissions (or Security)
Truecaller
Allow all permissions.
After that, go to additional settings > battery > manage apps battery usage, by default its ""standard"" make sure to keep it off."

"Steps for Android 9 and above:
Open your phone settings
Device care
App power management
Apps that won't be put to sleep
Add HappyMod to this list"

Navigate to your phone settings
Apps & Notifications
Apps
HappyMod
Battery
Launch > Disable Manage automatically - see picture below

Allow HappyMod to continue running when in background
Please go to Apps Manager / i Manager
Open Excessive background battery usage
Turn off HappyMod

Navigate to your phone settings
Apps & Notifications
Apps
HappyMod
Battery
Launch > Disable Manage automatically - see picture below

Navigate to your phone settings:
Battery
Battery optimization
Find HappyMod and choose "don't optimize".
1.) Battery

2.) Battery optimization

3.) Happymod

For HappyMod to work properly, you need to enable “auto start” from your system security settings. Please follow these steps:
Phone Manager -> Privacy Permissions -> Startup Manager -> Enable HappyMod
or
Security Center -> Startup Manager -> Enable HappyMod