Have you tried running these commands by hand? If not then that is the first thing I would try.

Do you know if sudo is working correctly? is the user account that you are logging in as listed in the sudoers file? (Or the equivalent sudoers.d/ directory on some systems

Is your user authorised to run su? The sysadmin of the remote box could have locked down sudo so that only certain known safe commands can be run. (Hardy anyone actually does this, because there are so many commands that can be abused in the wrong hands, so most sysadmins assume that anyone in the sudoers file can get root if they want it, and make sure that only trusted users are added to the file.)

Are you aware that root can read the crontab of any user, so you could also read a user's crontab with the command: sudo crontab -u <username> -l