You talking about the home, return, volume up/down......right?
In my car I need to go to factorysetting (8888+ok) and then panel key study, no 3, select the key on the screen and then hold the physical/mechanical key/ button for few seconds on your unit...you get a green square, do all and save.
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But don't know your unit, if that are mechanical buttons or touch software buttons...
I cant remember the function of touch learning button, no.2,, but you can try both..I thought I used that in an earlier version of Firmware to make buttons works again, but in latest I used panel key study.
My unit is a S8 with Opel front that match my dashboard with mechanical buttons around it ..
About the ISO plug, check if the supplied one with the unit matches that, on your linked Ebay there is a wiring specification...of the plug you stick in your unit...so the wires on other side you put in your ISO plug must correspond to that, but imaging you know that already ...
I have totally different plug, don't know if the power cable they supplied is an ISO connector that matches yours .
Other then that I don't know....contact supplier again, maybe defected unit ..