Rails 6.0.2.2what i did :

Question

Can't resolve image into URL: undefined method `attachment_url' for # Env: ruby : ruby 2.6.5p114

rails active_storage:install
rails db:migrate
has_one_attached :main_image
<%= f.label :main_image %>
<%= f.file_field :main_image %>
<%= image_tag event.main_image %>```