APIv1 - Banning, how to include a space in user_ban.public_reason

We deal with a lot of spam which results in moderators banning the member, clearing the IP field in the ban dialog and adding a note to the internal and external dialog boxes. 

To streamline this process I'm trying to see if the API can help and it does but I'm stuck when it comes to setting the external facing ban note user_ban.public_reason.  (supporting documentaton)

I cannot figure out how to include a space, eg. 'You've been banned for X reason'

<response status="error">
    <error code="100">
        <message>user_ban.public_reason: Contains one or more invalid characters. This field can contain letters, numbers, and special characters, such as dashes or underscores. Spaces are not permitted.
    </message>
    </error>
</response>

I've tried using +, ?, %20, %22... no dice, it fails each time. 

Is someone able to help a rookie out here - is this not possible or am I missing something obvious? 

The user story, as a admin I want to. ban a user using the API and set a external facing ban note that includes a space, e.g 'You've been banned for X reason'