Thanks for your response.
I followed your steps. When I select a list and click Confirm, the following error message displays:
Cannot add or update a child row: a foreign key constraint fails (
fk_j25_acym_user_has_list1 FOREIGN KEY (
id) ON DELETE NO ACTION ON UPDATE NO ACTION)
We changed the table prefix from j25_ to j4_ when we migrated the website from Joomla 3 to Joomla 4.
I have checked the database integrity under advanced configuration and got the green check.
Also, which is the correct format for the index:
j4_index_acym_list_has_mail1 or fk_j4_acym_list_has_mail1
Your assistance will be appreciated.