"On a USB stick" not selectable on installer

I’m using a Mac. When I get to the “install options” window, the radio button is set to “on an SD card” and the other options aren’t clickable. I’m trying to get OSMC going for the ATV.

Appreciate any feedback as I’ve been searching for an answer and haven’t been able to figure it out.

Just select the USB installer image

The SD card option isn’t selectable, it’s greyed out, so just click next

Thank you. I dIdn’t realise it was just a matter of clicking Next!