Loading image previews in blocked editor - cors error?

[Keiron]

Loving Twill so far, had a bit of an uphill battle to get Glide paths right and the media library work.

I've now moved on to blocks, following the videos on the tutorials page....

I've got a working media library and can see my images in there, the images have uploaded, but when it tries to generate the live preview of the block it's completely blank.

The console shows I'm getting CORS error:
Access to image at '' from origin 'http://admin.<domain.com>' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

Have I missed something in configuration here?