Similar problem with sc_apl_conf()

Like aka I have a similar problem with a detail form which is integrated in a master.

I have a table with columns id_a and id_b which I check with a sql query if a record exists

(in OnLoad of master form)

$query = "SELECT id_a, id_b FROM project WHERE id_a = [v_a] AND id_b = [v_b]";
    sc_select(dataset, $query);

if there is already a record with this criteria in the table I want my detail form my_detail_form shown only with a cancel button (not allowed to insert a new record)
if there isn’t a record in the table I would like to go directly in insert mode to make a new record.

if (false == {dataset})
        {
            // Record not found
            sc_apl_conf ("my_detail_form", "start", "new");        
        }

else
        {
            // Record found
            
            sc_apl_conf ("my_detail_form", "insert", "off");
        }

Summary is that the my_detail_form doesn’t go to the insert mode it only shows “no records found”.

What’s wrong?