That’s quite odd! I would recommend trying the same API call, but without specifying details about the file?
I would remove:
lastModified: new Date(),
type: "video/mp4",
I would also try out removing [blob] from the variable. Could you try that out and let us know if it worked? Just to make sure as well, is the Update ID with the ID of 7894482 an update you can edit within the UI?