Why cant i facetime without wifi iphone 11

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Good afternoon Marvelus7,

Welcome to the Apple Support Communities!

I understand you are trying to make a FaceTime call using cellular data instead of Wi-Fi on your iPhone 11 Pro Max. The resource below provides some troubleshooting steps for this issue. I've highlighted some key information here for you. Click on the link for complete details.

If you can't make a FaceTime call on your iPhone, iPad, or iPod touch

"If you're trying to use FaceTime over cellular, make sure that Use Cellular Data is on for FaceTime.

Go to Settings and tap Cellular or tap Mobile Data, then turn on FaceTime.

Go to Settings > FaceTime and make sure that FaceTime is on. 

• If you see "Waiting for Activation," turn FaceTime off and then on again. Learn what to do if you can't activate FaceTime.
• If you don't see the FaceTime setting, make sure that Camera and FaceTime aren't off in Settings > Screen Time > Content & Privacy Restrictions > Allowed Apps."

Take care.