Why is my MacBook saying that it is not charging but it is plugged in?

Try resetting the SMC https://support.apple.com/en-us/HT201295

Apple Portables: Troubleshooting MagSafe adapters

https://support.apple.com/en-us/HT203207

If your USB-C power adapter isn't charging your Mac notebook

https://support.apple.com/en-us/HT204652

Possibly:

• Faulty wall socket.
• Faulty cable.
• Faulty socket on Mac