Unable to download shared file with no password protection

To clarify, does the shared link itself refer to a particular file, or to a folder?

If it refers to a file, you should not supply the "path" parameter when calling /2/sharing/get_shared_link_file.

If it refers to a folder, you should supply the "path" parameter when calling /2/sharing/get_shared_link_file, and the value should be the relative path of the desired file inside the folder. So, for example, if the linked folder is named "Folder", and it contains a file named "File.ext", you would supply a "path" value of just "/File.ext". Or, as another example, if the linked folder is named "Folder", and it contains another folder named "Subfolder, and that "Subfolder" contains a file named "File.ext", you would supply a "path" value of "/Subfolder/File.ext".

If this still isn't working as expected for you though, please share the code and parameter values you're using so we can take a look. If you'd prefer to share privately, you can open an API ticket here. In either case though, do not share your access token.