MacBook Air not sleeping when closing lid

Why do you think it doesn’t sleep? How can you tell?

What is it doing when not sleeping, when you think it should sleep?

Do you have external devices connected, that might keep it awake?

Some behavioral details depend on macOS version (software capabilities), and/​or exact Mac laptop model (hardware capabilities). Please specify for your situation.

Find out which macOS your Mac is using - Apple Support

Identify the model of your Apple device - Apple Support

Have you reviewed the Battery System Settings? There are some settings and options there that may influence aspects of sleep mode.

"why my macbook won't sleep when i close the lid"

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Getting Mac to Sleep wen Closing the Lid:

Try doing BOTH of the following...

A. Select "Never":

1. Open: System Settings
2. Click: Apple menu
3. Select: System Settings 
4. Click: on Lock Screen in the side bar 
5. Select "Never" for: "Turn display off on battery when inactive" and "Turn display off on power adapter when inactive". 

B. Prevent Automatic Sleeping: 

1. Click: Battery
2. Click: Options
3. Check: "Prevent automatic sleeping on power adapter when the display is off". 
4. Click: Done to save the changes

Source: mac turn off sleep mode