why face id not working in my device

According to Apple:

Using diagnostics available in iOS 14.6 or later, Apple has detected an issue with your TrueDepth camera that might cause it to not function as expected. The TrueDepth camera contains lasers, which might be disabled for safety reasons if the device malfunctions or is damaged. This won't prevent you from using your iPhone or iPad, but until your iPhone or iPad is updated or serviced, you might not be able to use Face ID, Animoji, Memoji, and some other features that use the front camera.

As a result, I recommend service.

Service Checklist:

• iPhone service pricing.
• Check AppleCare Coverage.
• Get your iPhone ready for service.

Click ▶︎ Start a Service Request. ⚛️

Need more help?

• Call Apple Support at 1-800-APLCARE. 📞
• International Support. 🌐
• Contact Apple Support. 📝
• Chat using Messages. 💬

Click ▶︎ Check Repair Status. 🔧

It can occur that you will receive the following message on your iPhone or iPad Pro : " A problem was detected with the true depth camera, FaceID is disabled"

When you're getting this error message, Make sure that you're iPhone or iPad Pro is running the latest version of iOS or iPadOS. If your device is running the latest iOS or iPadOS and you're still getting this message and FaceID is not working:  contact Apple Support to get your device serviced.