Hello! Please add to OPACAuthorIdentifiers "MARC21 only" in cgi-bin/koha/admin/preferences.pl?tab=opac#opac_Features In Unimarc "Display" leads to an error. Later I looked in https://koha-community.org/manual/23.05/en/html/opacpreferences.html#opacauthoridentifiers. Good Luck! Igor A. Sychev Tomsk Polytechnic University https://lib.tpu.ru