Use a 15W USB-C charger and let it charge for at least an hour before setting them up in the app.

Thanks Rashi, but they won't charge at all, the orange light flashes once and goes off, then no lights at all. A couple of times I've plugged them in and I get a two second orange, then blue, then nothing, so I left them like that for a couple of hours yesterday and still no charge.

How many watts is the charger you are using?

15 watts 

It sounds like you may have a defective pair of headphones. I would return it and exchange for a new pair.

Yeah I think you're right, really disappointed with them, thanks for your advice...

So after a while on the phone to Sonos, it was decided that they were faulty, and I should return them, to POLAND? I sent them via UPS with the supplied label on Monday from the UK, and tracking says that they won't be delivered until Thursday, which means that by the time Sonos has inspected them etc, they won't send the replacement pair until Friday at the earliest, which probably means that I won't receive them until the following week.

Guys that means after parting with my money, I actually don't get to use my new headphones until almost two weeks after I paid for them, and that's assuming the second pair work, disgusting service from Sonos, not even an apology, I so wish I hadn't brought them now, and I'd taken the negative reviews more seriously ...

Did you manage to get new Ace? You like?

After purchasing a pair, I really found my experience much better than all the bad ones people were sharing.

Really wonder if people had high expectations? I can definitely appreciate the disappointment of how the Ace did not connect and run off wi-fi like Sonos speakers do. That would been so very nice.