my Face ID isn’t working on my iphone X

Yes, it did fail. Whoever replaced your battery damaged the TrueDepth camera when they were performing the replacement.

If the battery was replaced at a Genius Bar or Apple authorized service center, the take it back and have them fix it.

If this was a third party repair shop, you're on your own. Apple won't repair it now .

This is generally a hardware issue. If the unit's on an OS version older than 16.5.1, you might be able to fix it by updating it from a computer or the Software Update function in Settings; otherwise, contact Apple Support.

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