I use this command on my LAMP, and works on LLMP as well with CRON outputs to Emails.
on MAMP try this command see if this works
*/5 * * * * /usr/bin/curl --silent --compressed http://localhost:8888/moodle/admin/cron.php
or you can as well try
*/5 * * * * /usr/bin/curl --silent --compressed http://localhost:8888/moodle/admin/cli/cron.php
as well try getting rid of --compressed command if it doesnt worked out.