User with custom add permissions unable to add the item to SharePoint online list

Question

We are having a SharePoint list in which user is unable to add the list item even when the user has the "Add" permissions on the site as well as on list.

The list does not have any Item level permissions or unique permissions. Yet whenever we try to add any item in that particular list we are getting below error:

Access denied. You do not have permission to perform this action or access this resource while adding item to SharePoint list.

Now the same user is able to add the list item for other lists.

Answer 1

Whether this issue occurs on all users? Please provide some screenshots of custom permission.

You could try to remove user permissions then re-add.