I want to populate filtered value from one doctype to another

I want to filter the Employees to Sales Order where the employees Designation is “Zonal manager

How can i filter the employees ?

The Customer have custom field called Zonal Managers i want to populate values in there

frappe.ui.form.on('Customer', {
    onload: function(frm) {
        // Fetch and populate Zonal Managers when the form is loaded

function fetchAndPopulateZonalManagers(frm) {
    // Query Employees with designation 'Zonal Manager'
        method: 'frappe.client.get_list',
        args: {
            doctype: 'Employee',
            filters: {
                designation: 'Zonal Manager'
            fields: ['employee', 'employee_name']
        callback: function(response) {
            if (response.message && response.message.length > 0) {
                // If Zonal Managers found, populate the field
                let zonalManagers = response.message;
                let zonalManagerOptions = [];
                zonalManagers.forEach(function(manager) {
                        'label': manager.employee_name,
                        'value': manager.employee
                // Set options for Zonal Manager field
                frm.set_df_property('custom_zonal_managers', 'options', zonalManagerOptions);
            } else {
                // No Zonal Managers found, show a message
                frappe.msgprint(__('No Zonal Managers found.'));

This code is not working can any one help