With a nested routes like that,

get_barcode_ticket_orders POST   /tickets/:ticket_id/orders/get_barcode(.:format) orders#get_barcode

You would need to also pass the parameter ticket_id into the data hash.  Is the ticket_id available at this point? If so, you could pass it into a data attribute and access it in the JS. Otherwise, you may want to reconsider the routes to look something like this (or similar):

resources :tickets do
  resources :orders
end
post '/orders/get_barcode',  as: :get_barcode, controller: :orders, action: :get_barcode
# get_barcode POST   /orders/get_barcode(.:format)         orders#get_barcode