How to use tap tempo on samples?

I have a sample in the editor and am trying to tap in the tempo but there is nothing to show that the tempo is being recorded - it just stays stuck. TT is flashing.

What might I be doing wrong here?

All the videos I've seen show their tap tempo working as normal, so they haven't helped solve the mystery.

When you Tap Tempo, Observe the Tempo on the Main Screen. Then go to Sample edit to adjust