So I am using Nucleo64 (303RE) board for USB HID mouse project.
As you know, it does not have second USB port for USB applications but it does have PINS that can act as DM, DP (USB minus, plus data).
When I configured everything, I run debug and it was telling me that packet has been send successfully, but I could not see any signal on oscilloscope. NOTE that I checked clock output for USB and it was a good looking 48MHz clock.