In some cases, we have observed that the virtual keyboard on HP Engage Pro / Essential is available when logging into Windows, but not when logging into the retail7 POS software itself.
If this happens, one possibility is that the virtual keyboard driver crashed. To avoid this, the driver must be updated.
HP offers the HP Image Assistant (or HPIA for short), to generally check which drivers need to be updated. It can be downloaded from https://ftp.ext.hp.com/pub/caps-softpaq/cmit/HPIA.html and checks the entire hardware for necessary updates after installation.
After installing the updates, the problem is solved.