iPhone 12 Pro Max isn’t charging

This could be because of many reason, 1) your charging port could be dirty 2) your charging port could have liquid in it or 3) it may be damaged, requiring you to get service on it.

Here's the Apple Support article on it: If your iPhone or iPod touch won't charge - Apple Support

Please read the following article then post back with your question.

Writing an effective Apple Support Communities question

Writing an effective Apple Support Commun… - Apple Community

Hi, if you have checked that you've connected the phone's charging wire correctly, then you may check with another charging wire to see whether it is the wire's problem or the charging port of the phone's problem. If it is not the problem of the charging wire or the charger, you can ask Apple Support(iPhone Repair - Official Apple Support) for the problem, or ask to repair the phone at Genius Bar: Genius Bar Reservation and Apple Support Options - Apple.

If you need another charger: Buy iPhone Accessories - Apple.

Charleneblakes Said:

"My phone isn’t charging"

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Troubleshooting iPhone Charge:

Visit the following links for tips on troubleshooting this...

I. Try what is on this Link: If your iPhone, iPad, or iPod touch won't Turn on or is Frozen - Apple Support

II. View the Battery Health:

Apple recommends you get a new battery, once the Battery Health reaches 80% or lower. When the Battery Health is 80% or lower, it is time for a new battery.

1. Go To: Settings
2. Tap: Battery
3. Tap: Battery Health
4. View: [the percentage]
5. Is it 80% or less?  If so, it is time for a new battery.

III. Perform a Restart:

Try Force Restarting your iPhone. Save any information that need be. Then perform the restart.

Go Here: Force Restart iPhone - Apple Support

IV. A Few Apple Support Sites that May Help:

• iPhone Battery and Performance - Apple Support

• Charge and Monitor the iPhone Battery - Apple Support

• About the Battery Usage on your iPhone - Apple Support

• If your iPhone or iPod touch won't Charge -Apple Support

• About Optimized Battery Charging on your iPhone - Apple Support

• If you See "Your iPhone Battery may Need to be Serviced" - Apple Support

• Use Low Power Mode to Save Battery Life on your iPhone - Apple Support

What happens when you try?

Have you tried a different cable and/or charger?