Unable to add fingerprint on my iPhone 8

If you have followed the instructions in the message and Touch ID is still not working, this is likely a physical or hardware issue with the Home Button. I would recommend service at your nearest Apple Store's Genius Bar or an Apple Authorized Service Provider.

Genius Bar Reservation: Genius Bar Reservation and Apple Support Options - Apple

Apple Authorized Service Provider Reservation: Find Locations

themba181 wrote:

https://discussions.apple.com/content/attachment/69fa71f0-26a9-4426-b1ef-e369040866f9

follow the instruction in the screenshot you posted