Face ID is broken

See this support article:--> If Face ID isn't working on your iPhone or iPad Pro - Apple Support

and/or this one:--> If an alert says Face ID has been disabled on your iPhone or iPad Pro - Apple Support

If, after performing all the steps provided in the above support articles, the issue persists, contact Apple Support directly, using this specific link:--> Apple Support , or make an appointment and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple - Find Locations - Location Selector. After checking it out, they'll give you all the available options.

Regards

Giulio

Make an appointment at the Genius Bar of your local Apple Store. The phone will most likely have to be replaced.

Liquid damage is not repairable.