What is Attribute?
Attribute is a collection of key/value pairs following the pattern “NAME”:“John”. All are assumed to be strings. These attributes will apply to the html content of the body of your email, sender name and subject parameters. The total collective size of your attributes may not exceed 10,000 bytes per personalization object in the API call.
Attributes to be used in your HTML as [%NAME%] for NAME , [%AGE%] for AGE. Only special character: underscore is allowed. Attribute should not contain any spaces.