Enter the ADS Journal bibcode exactly as it is displayed in the URL of the paper related Abstract Service page in the 'bibcode=' statement.
For example, if the ADS abstract URL is
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...365L...1J&db_key=AST&...
you should specify here only
2001A%26A...365L...1J