If blobs are supported (not sure if not)
But extensions are uplaoded into
A sub folder, and you tried to load the blob from the “root” of the domain instead of the same folder. You need to use a relative link to your resource, not an absolute link.
There is not file at :https://my-ext-subdomain.ext-twitch.tv/f2393609-c468-439f-a5bd-62e23142e138 so it 404’ed and the 404 page didn’t include CORS headers, so you got a misleading error
Edit: additional notes from Discord, blobs may be disallowed as they fall under the eval rule and evals are not allowed
Section 2.6 https://dev.twitch.tv/docs/extensions/guidelines-and-policies