Navigation: ADMIN > SETTINGS > Client Portal Settings from the sub menu
The ability for clients to cancel scheduled jobs is by default "allowed" in your client portal settings.
If for some reason this option has been unchecked, you will need to re-check it if you would like to offer this option.
Look at the option to "Allow clients to cancel jobs" in the "Client Portal Settings"
If this box is UNchecked, check it again
When you now go into the client portal, the option to cancel a job from a client's schedule is now available.