it is a common problem, as it seems that he box.com shared folder is not a typical website, like https://beta.rclone.org.
there might be a workaround, tho as i do not use box, i would not know.
have you searched the forum, for example
https://forum.rclone.org/t/rclone-copy-shared-box-folders-files-to-local-filesystem/22532