Similar to the "Reference ID" field, the Custom 1, 2, and 3 fields are only used during the import process to preserve important data from old systems that may be needed in the future.
NOTE: We don't display these fields anywhere except when you are editing a customer record or exporting data; and we don't recommend building systems that rely on these fields.
FROM THE WEB APP
FROM THE MOBILE APP
These fields are only available from the web app at this time.