My fingerprint sensor is not working

Have you replaced the display?

According to reddit you'll need to recalibrate the sensor if you have.

I'd also recommend cleaning the scanning area with a Microfiber cloth to ensure accurate reading.

"To access the calibration menu you need to:

Go to settings > About phone > All specs > repeatedly tap Kernel version until the calibration menu appears > tap the menu button in the top-right corner > Additional tools > 6. Fod fingerprint calibration.

Follow the steps on the screen. The first test is to hold a white cloth/paper over the fingerprint sensor. The second test is a black cloth/paper. The third test, just use your bare finger.

If it says "Test successful" at the end, the fingerprint sensor should be ready to use. If the test fails, try again. I read a forum post where someone had to try three or four times before it passed."

If recalibration doesn't fix the issue I'd recommend a visual inspection of the internal hardware.