= effective_form_with(model: [:admin, stamp], engine: true) do |f|
  - if f.object.new_record?
    = f.select :owner, { 'Users' => current_user.class.members.sorted }, polymorphic: true
  - else
    = f.static_field :owner

  = render 'effective/stamps/fields', f: f, stamp: f.object

  - if f.object.new_record?
    = f.submit 'Save and Mark Paid'
  - else
    = f.submit 'Save'