The uploading and creating processes both respond with status code '200', but the uploaded CR3 and HIF files receive an error message ("Failed: There was an error while trying to create this media item") in the Google Photos app and website. JPEG and CR2 files upload successfully. It's worth noting that I can successfully upload CR3 files with the Google Photos web interface.
I checked access token permissions, album ID, and JSON request body, which appear to be correct. I expect the CR3 and HIF files to upload successfully and be viewable in the Google Photos app and website. I am wondering if these file types are supported by the Google Photos API, and if there might be any other reasons why the upload is failing for these file types.
Why do you expect that? CR3 is a raw file, lots of data but not cooked. For Google to show you a picture would require it to make a lot of editing decisions, or use the JPDG thumbnail embedded in it. Why not just upload that JPDG, unless you've done your edit and have a different resukt in which case upload that.
HEIF I know little of, except that iPhones will produce them if asked.