backend returns if user is already subscribed

db/migrate/20191127233735_add_product_to_customer.rb

@@ -0,0 +1,5 @@
+class AddProductToCustomer < ActiveRecord::Migration[6.0]
+  def change
+    add_column :discourse_patrons_customers, :product_id, :string
+  end
+end

db/migrate/20191128044206_remove_customer_index.rb

@@ -0,0 +1,5 @@
+class RemoveCustomerIndex < ActiveRecord::Migration[6.0]
+  def change
+    remove_index :discourse_patrons_customers, :customer_id
+  end
+end