Hi, On user event script I am trying to add column to a sublist (Item Group record):

const beforeLoad = (scriptContext) => {

            if (scriptContext.type === scriptContext.UserEventType.VIEW || scriptContext.type === scriptContext.UserEventType.EDIT) {
                let form = scriptContext.form;
                let componentsSublist = form.getSublist('member');

                log.debug('componentsSublist', JSON.stringify(componentsSublist));

                componentsSublist.addField({
                    id: 'custpage_test',
                    type: serverWidget.FieldType.INTEGER,
                    label: 'Test'
                });
            }
}

But I can see the field only on EDIT, and also when I set value to that field its not save it and the field disappear after saving the record (VIEW) Any solution?

Fields added in that way are not permanent and do not persist. You need to add an actual custom field via the UI

But I have to do it inside the sublist that cant be change in UI so I cant?

you could serialize the values in the sublist to a custom body field on save and deserialize on beforeLoad