Good day. I was trying to upgrade Koha from version 18.06 to 21.05 on Ubuntu 20.05. I installed Ubuntu 20.04 and then installed Koha 20.05. I then used the Koha 18.06 database dump to restore the Koha database after dropping the Koha 20.05 database. On trying to do the database schema upgrade, I am getting the following error: The following error occurred while importing the database structure: DBD::mysql::st execute failed: Referencing column 'message_transport_type' and referenced column 'message_transport_type' in foreign key constraint 'borrower_message_transport_preferences_ibfk_2' are incompatible. at /usr/share/perl5/DBIx/RunSQL.pm line 279, <$args{...}> line 1. Something went wrong loading file /usr/share/koha/intranet/cgi-bin/installer/data/mysql/kohastructure.sql ([SQL ERROR]: CREATE TABLE `borrower_message_transport_preferences` ( `borrower_message_preference_id` int(11) NOT NULL DEFAULT 0, `message_transport_type` varchar(20) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '0', PRIMARY KEY (`borrower_message_preference_id`,`message_transport_type`), KEY `message_transport_type` (`message_transport_type`), CONSTRAINT `borrower_message_transport_preferences_ibfk_1` FOREIGN KEY (`borrower_message_preference_id`) REFERENCES `borrower_message_preferences` (`borrower_message_preference_id`) ON DELETE CASCADE ON UPDATE CASCADE, CONSTRAINT `borrower_message_transport_preferences_ibfk_2` FOREIGN KEY (`message_transport_type`) REFERENCES `message_transport_types` (`message_transport_type`) ON DELETE CASCADE ON UPDATE CASCADE ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci ) at /usr/share/koha/lib/C4/Installer.pm line 580. Any pointers will be greatly appreciated. Kind Regards,