Friendly Boffin and I spent several hours over this thing.
The jack socket in the adapter was floating almost free. (Three tags having insufficient and failed solder to board joints).
Probably grandaughter's annoyance at intermittant failure, leads in the jackplug had broken.
Careful tracing and trial produced a flashing red LED in the sensor becoming steady for a few seconds before going out.
No response from using remote control.
Verdict - To the bin!
This item had a very short sales life and though a few are currently on eBay, I have the uncharitable thought that the original production had a mighty failure rate lasting just about the critical 1 year.