by Jason Caldwell » April 20th, 2011, 11:55 pm
Thanks for the excellent question.
It depends on which Payment Gateway you're using. As far as s2Member is concerned though, s2Member treats this field as raw text. That is, there are NO validation routines passed against this field. It may hold a string with any characters, including multibyte characters even, and with any length.
* It will never start or end with a space though.
s2Member always trims leading and trailing white space.
In the case of PayPal,
a Paid Subscr. ID would look something like this:
I-JSEC34JDCK334J