Add custom menu item and endpoint to WooCommerce my-account page

add-custom-menu-item-and-endpoint-to-woocommerce-my-account-page.php

/* Add custom menu item and endpoint to WooCommerce My-Account page */

function my_custom_endpoints() {
    add_rewrite_endpoint( 'refunds-returns', EP_ROOT | EP_PAGES );
}

add_action( 'init', 'my_custom_endpoints' );

// so you can use is_wc_endpoint_url( 'refunds-returns' )
add_filter( 'woocommerce_get_query_vars', 'my_custom_woocommerce_query_vars', 0 );

function my_custom_woocommerce_query_vars( $vars ) {
	$vars['refunds-returns'] = 'refunds-returns';
	return $vars;
}

function my_custom_flush_rewrite_rules() {
    flush_rewrite_rules();
}

add_action( 'after_switch_theme', 'my_custom_flush_rewrite_rules' );

function my_custom_my_account_menu_items( $items ) {

	$new_item = array( 'refunds-returns' => __( 'Refunds & Returns', 'woocommerce' ) );
	
    // add item in 2nd place
	$items = array_slice($items, 0, 1, TRUE) + $new_item + array_slice($items, 1, NULL, TRUE);

    return $items;

}

add_filter( 'woocommerce_account_menu_items', 'my_custom_my_account_menu_items' );

function my_custom_endpoint_content() {
    wc_get_template( 'myaccount/refunds-returns.php');
}

add_action( 'woocommerce_account_refunds-returns_endpoint', 'my_custom_endpoint_content' );

This was really helpful, thank you!

A note for anyone here in future: make sure you flush your permalinks after adding the code, or else your new endpoint will 404.