Transverse - Halion Sonic SE

I am using Cubase 12 with halion sonic se with Transverse. I selected White Square as my instrument and entered some midi notes into my sampler.
My issue is that the sound will not stop unless I close Cubase. If I adjust the velocity, Play the notes it is the same. Just humming in the background.
What can I do to stop this without switching off.
many thanks