Is there somewhere full list of supported URL for configuration upload/download? Documentation mentions FTP and HTTP (in example only - nowhere is it stated explicitly). Some BURTs mention also TFTP and HTTPS/FTPS 🙂
Today FTP is often disabled and HTTP requires some setup that is not always present. Using SCP/SFTP would be the most simple option but from quick test (8.2.1 SIM) it is not recognized.