Upgraded stereo not working

Hi everyone, wondering if someone could help, I have a 2004 FL1 HSE 1.8. When I purchased it a few months ago it had the original stereo which had a very basic Sat nav system, it was all working fine but I wanted to upgrade it so I purchased a touch screen stereo with Apple CarPlay, got it installed using the original wiring harness. All works great, connected my phone and everything works UNTIL I actually put the car in gear, now the upgraded stereo does have video input for a reversing camera which I planned to install at a later date but when I put the car in gear it’s still working fine, once I begin to move the stereo switches off and then restarts and very briefly the screen goes into reversing mode, then it switches off again and continues to do the same loop until I’m stationary again, then as before it all works fine, once I pull off again it goes back to the restarting, reversing loop.
So I thought it might be the unit I brought (got it off eBay, looks Chinese, so thinking it might be duff) I then went through my garage and found an old aftermarket Sony CD player from years back, plugged that in, again with the original wiring harness and it also doesn’t work. I have tried this out on my Toyota and it works fine so I’m now left thinking it must be something to do with the car and it having that basic Sat Nav function.
Has anyone experienced this or am I doing something wrong
Thanks in advance for anyone who can help