Rails: dynamic select on multistep form not keeping selected

I am working on a multistep form for an order placement process following Ryan Bates's Multistep Tutorial #217 which uses a session. On the first step I have two select fields: one for countries (land) and a dynamic one for shipping services. After a land has been selected the shipping services are loaded into the second select field through javascript/jQuery and the total price is calculated again through JS.

app/views/orders/_shipping_step.html.erb

<%= f.collection_select(:land_id, Land.all, :id, :name, {:prompt => "select a country"}, {:id => 'lands_select'}) %>
<%= f.select(:shippingservice_id, options_for_select(@shippingservices.collect { |s| [s.name.titleize, s.id, {'data-price' => s.price}] }, :selected => f.object.shippingservice_id), {:prompt => "select a carrier"}, {:id => "shippingservices_select"}) %>

ajax script

$(document).on("change", "#lands_select", function(event){
  $.ajax({
    url: "/carts/update_shipping/" + event.target.value,
    type: "GET",
  })
});

On the shipping details step of the multistep form I can choose a land, the corresponding options for shipment are loaded and I can choose one. When progressing to the payment step, I can place the order and everything works, but in case I want to return from the payment step to the order step to change something, the shipping services selector displays options for land_id = 1, while the land select displays the choose country, for example id 84.

I added :selected => session[:cart_params]) to the shipping service select, but it does not appear to be working. :selected => f.object.shippingservice_id keeps priority or standard shipping options, but for Land_id 1.

How can I get this working? Is it the select field or the JS? Why doesn't the second select keep the chosen land in memory?

Thank you in advance!

LOG:

Started GET "/orders/new" for 127.0.0.1 at Thu Dec 27 22:08:52 +0100 2018
Processing by OrdersController#new as HTML
  Cart Load (0.3ms)  SELECT `carts`.* FROM `carts` WHERE `carts`.`id` = ? LIMIT 1  [["id", 1]]
  Land Load (1.4ms)  SELECT `lands`.* FROM `lands` 
  CartItem Load (0.3ms)  SELECT `cart_items`.* FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.2ms)  SELECT MAX(`cart_items`.`length`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.2ms)  SELECT MAX(`cart_items`.`width`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
  CACHE (0.0ms)  SELECT `lands`.* FROM `lands` 
  Shippingservice Load (0.6ms)  SELECT `shippingservices`.* FROM `shippingservices` INNER JOIN `zones` ON `zones`.`id` = `shippingservices`.`zone_id` INNER JOIN `lands_zones` ON `lands_zones`.`zone_id` = `zones`.`id` INNER JOIN `lands` ON `lands`.`id` = `lands_zones`.`land_id` WHERE `lands`.`id` = 1 AND (weightmin <= 50 AND weightmax >= 50 AND heightmin <= 3 AND heightmax >= 3 AND shippingservices.shippingcarrier = ‘1’) AND (lengthmax >= 210 AND widthmax >= 149)
  Product Load (0.3ms)  SELECT `products`.* FROM `products` WHERE `products`.`id` = 3 LIMIT 1
  Hero Load (0.2ms)  SELECT `heros`.* FROM `heros` WHERE `heros`.`id` = 18 LIMIT 1
  Rendered orders/_shipping_step.html.erb (13.7ms)
  Rendered orders/new.html.erb within layouts/application (16.2ms)
  Rendered layouts/_header.html.erb (0.1ms)
  Rendered layouts/_footer.html.erb (0.1ms)
Completed 200 OK in 44ms (Views: 23.0ms | ActiveRecord: 3.9ms)

Progressing to the payment step:

Started POST "/orders" for 127.0.0.1 at Thu Dec 27 22:09:33 +0100 2018
Processing by OrdersController#create as HTML
  Parameters: {"order"=>{"ship_to_last_name"=>”surname”, "ship_to_address"=>”street”, "ship_to_city"=>”city”, "ship_to_postal_code"=>”postcode”, "phone_number"=>”somenumber”, "shippingservice_id"=>"27", "email"=>”something@example.tld”, "land_id"=>"85", "ship_to_first_name"=>”firstname”}, "authenticity_token"=>”somestring”, "utf8"=>"✓", "commit"=>"Continue"}
  Cart Load (0.2ms)  SELECT `carts`.* FROM `carts` WHERE `carts`.`id` = ? LIMIT 1  [["id", 1]]
  Land Load (1.5ms)  SELECT `lands`.* FROM `lands` 
  CartItem Load (0.4ms)  SELECT `cart_items`.* FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.2ms)  SELECT MAX(`cart_items`.`length`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.2ms)  SELECT MAX(`cart_items`.`width`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
  Land Load (0.4ms)  SELECT `lands`.* FROM `lands` WHERE `lands`.`id` = 85 LIMIT 1
  Shippingservice Load (0.3ms)  SELECT `shippingservices`.* FROM `shippingservices` WHERE `shippingservices`.`id` = 27 LIMIT 1
  Product Load (0.3ms)  SELECT `products`.* FROM `products` WHERE `products`.`id` = 3 LIMIT 1
  Hero Load (0.3ms)  SELECT `heros`.* FROM `heros` WHERE `heros`.`id` = 18 LIMIT 1
  Rendered orders/_payment_step.html.erb (7.0ms)
  Rendered orders/new.html.erb within layouts/application (8.9ms)
  Rendered layouts/_header.html.erb (0.1ms)
  Rendered layouts/_footer.html.erb (0.0ms)
Completed 200 OK in 39ms (Views: 13.7ms | ActiveRecord: 4.6ms)

Selecting the shipping country:

Started GET "/carts/update_shipping/85" for 127.0.0.1 at Thu Dec 27 22:09:27 +0100 2018
Processing by CartsController#update_shipping as */*
  Parameters: {"id"=>"85"}
  Cart Load (0.2ms)  SELECT `carts`.* FROM `carts` WHERE `carts`.`id` = ? LIMIT 1  [["id", 1]]
  Land Load (66.9ms)  SELECT `lands`.* FROM `lands` 
  CartItem Load (0.4ms)  SELECT `cart_items`.* FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.2ms)  SELECT MAX(`cart_items`.`length`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.2ms)  SELECT MAX(`cart_items`.`width`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
  Shippingservice Load (0.6ms)  SELECT `shippingservices`.* FROM `shippingservices` INNER JOIN `zones` ON `zones`.`id` = `shippingservices`.`zone_id` INNER JOIN `lands_zones` ON `lands_zones`.`zone_id` = `zones`.`id` INNER JOIN `lands` ON `lands`.`id` = `lands_zones`.`land_id` WHERE `lands`.`id` = 85 AND (weightmin <= 50 AND weightmax >= 50 AND heightmin <= 3 AND heightmax >= 3 AND shippingservices.shippingcarrier = ‘1’) AND (lengthmax >= 210 AND widthmax >= 149)
  Rendered carts/_shippingservice.html.erb (0.2ms)
  Rendered carts/update_shipping.js.erb (2.9ms)
Completed 200 OK in 87ms (Views: 7.8ms | ActiveRecord: 68.6ms)

Returning to the shipping details step:

Started POST "/orders" for 127.0.0.1 at Thu Dec 27 22:09:35 +0100 2018
Processing by OrdersController#create as HTML
  Parameters: {"authenticity_token"=>”somestring”, "utf8"=>"✓", "back_button"=>"Back"}
  Cart Load (0.3ms)  SELECT `carts`.* FROM `carts` WHERE `carts`.`id` = ? LIMIT 1  [["id", 1]]
  Land Load (2.4ms)  SELECT `lands`.* FROM `lands` 
  CartItem Load (0.5ms)  SELECT `cart_items`.* FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.3ms)  SELECT MAX(`cart_items`.`length`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.4ms)  SELECT MAX(`cart_items`.`width`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
  CACHE (0.0ms)  SELECT `lands`.* FROM `lands` 
  Shippingservice Load (0.7ms)  SELECT `shippingservices`.* FROM `shippingservices` INNER JOIN `zones` ON `zones`.`id` = `shippingservices`.`zone_id` INNER JOIN `lands_zones` ON `lands_zones`.`zone_id` = `zones`.`id` INNER JOIN `lands` ON `lands`.`id` = `lands_zones`.`land_id` WHERE `lands`.`id` = 1 AND (weightmin <= 50 AND weightmax >= 50 AND heightmin <= 3 AND heightmax >= 3 AND shippingservices.shippingcarrier = ‘1’) AND (lengthmax >= 210 AND widthmax >= 149)
  Product Load (0.3ms)  SELECT `products`.* FROM `products` WHERE `products`.`id` = 3 LIMIT 1
  Hero Load (0.2ms)  SELECT `heros`.* FROM `heros` WHERE `heros`.`id` = 18 LIMIT 1
  Rendered orders/_shipping_step.html.erb (16.5ms)
  Rendered orders/new.html.erb within layouts/application (18.4ms)
  Rendered layouts/_header.html.erb (0.2ms)
  Rendered layouts/_footer.html.erb (0.1ms)
Completed 200 OK in 109ms (Views: 24.0ms | ActiveRecord: 5.1ms)