The Feodora Installation Guide, for example, what is published at:
https://docs.fedoraproject.org/f28/install-guide/install/Preparing_for_Installation.html
and
https://docs.fedoraproject.org/f27/install-guide/install/Preparing_for_Installation.html
correctly shows the differing command name for SHA 256 verification, but needs to
cope with how the Mac shasum uses a different syntax for the CHECKSUM file.
(This is documented in, for example, Red Hat bugzilla 1297453.)

To remedy this problem change:

For OSX:
$ shasum -a 256 -c *CHECKSUM

to

For OSX:
$ grep '^SHA256' *-CHECKSUM | awk -F '[()=]' '{ print $4 " " $2 }' | shasum -a 256 -c

This will re-format the contents of the file to comply with what shasum needs.