Why Sales Order Item showing Item rate 0?

In already created Sales Order if I’m updating Item from Sales Order Item then I’m getting rate=0 as well amount is 0.0.

I could not see any error log in browser console.

frappe.ui.form.on("Sales Order Item", {
    item_code: function (frm, cdt, cdn) {
      let row = frappe.get_doc(cdt, cdn);
      
      frm.doc.items.map((item) => {
        frappe.db.get_value("Item", {'item_code': item.item_code}, ['sku', 'standard_rate']).
        then(r => {
          let values = r.message;
          row.item_sku = values.sku
        })
      });
    },
})