We've noticed that CG has stripped + symbols from customer emails to use as their code.
We're not providing Cheddar with a specific customer code when redirecting a user to the Hosted Payment Page, we're just providing an email. The documentation states that the email will be used as the customer Code in the absence of one.
However, we've noticed that when a user's email has a + symbol in it (eg. [email blocked]), that + is replaced with a space on the code. We can go in and manually change that space back to a +, so it doesn't seem to be a limitation on characters for a customer code.

#1 Posted by Marc Guyer Support staff on 30 May, 2012 05:20 PM
A raw plus sign is a urlencoded space character. So, if you pass it in and it should be a literal plus sign, you'll need to urlencode it as a plus sign.
Dean closed this discussion on 23 Jan, 2013 01:48 PM.