Electric G Line Rear Wheel Not Spinning Freely

Hi. I'm definitely not a bike mechanic, and this is the first electric bike I've owned, so I may be missing something simple.

The rear wheel doesn't spin freely, likely putting more strain on the battery (and my legs).

I've tried adjusting the brake to give more room (no difference) and adjusting the rear axle bolts(no difference).

I'd read that these hubs may be stiff at first, but even though I don't use the bike often I've still done a few 20-40 mile rides.

Is there something I'm missing, or do I just need to find an official Brompton service partner to have a look?

Thanks!