How can I delete pasted images from

When I add screenshots, I typically will paste them from the clipboard into the GH editor window. Sometimes there are ones that I replace immediately or that have info that isnt supposed to be public.

I want to delete these. I tried doing a DELETE using http basic auth and a PAT but it tells me
InvalidArgumentUnsupported Authorization TypeAuthorizationBasic Og==R71...

How can I delete these images?