Rianu allows you to set unlimited custom data on a subscriber. These fields are great for storing addition information.
Create Custom Fields
To create a custom field. Go to Settings.
A list will be shown of all your custom fields.
Enter the name of the field you want.
Use Custom Field in API
Using the Custom field in the API is straight forward.
Find the code for the custom field.
Add the code plus the data to the JSON in the Subscribercreate / subscriberupdate API calls "_cdIJAXL40:" "November"