Dell S2340T with Surface 3

I have a new Dell S2340T touchscreen monitor and a Surface 3 (love it). If I connect the two via a DisplayPort cable I can mirror the S3 screen readily. However the touchscreen capability isn't operative on the monitor as I assume it should be.

I've gone to the Dell site and installed the driver for the monitor - and rebooted.. No luck.
I've looked at the monitor instructions both onscreen and in the manual. No luck

Any suggestions on how to get it working would be much appreciated.