Okay, we found the issue.
If you look at the generated “Identifier” for the Popup in the Popup Action dialog, you’ll see that the identifier is 8oTL/TGk.
When we attempt to upload the file, we generate a request URL which contains the path of the component making the request. When the request is received, the system verifies against the location of the component. When the component is in a Popup, the identifier is part of the path we check against; the inclusion of the / character as part of the identifier results in an added layer within the path, and so the verification fails.
I’ll open a ticket to verify we don’t allow the \ character to be generated as part of an identifier for Popups.
Workaround:
Replace the \ character within the identifier with any letter or number, or better yet supply your own identifier which means something to the Popup, like popup-camera. Supplying your own ID allows you to use other actions to close/toggle the Popup as needed.