Julian's multi-step validations state machine

aasm.rb

aasm do
  state :invited, initial: true
  state :identified
  state :details_added
  state :bank_details_added
  state :completed

  event :identify do
    transitions from: :invited, to: :identified
  end

  event :add_details do
    transitions from: :identified, to: :details_added
  end

  event :add_bank_details do
    transitions from: :details_added, to: :bank_details_added
  end

  event :complete do
    transitions from: :bank_details_added, to: :completed
  end
end

validations.rb

validates :company_name, :address, :country, :zip, :city,
          :trade_certificate, presence: true, on: :add_details

validates :terms_of_service, acceptance: true, on: :complete

view.html.erb

= render 'devise/registrations/activation/step_1_identification' if @partner.invited?
= render 'devise/registrations/activation/step_2_details' if @partner.identified?
= render 'devise/registrations/activation/step_3_bank_account' if @partner.details_added?
= render 'devise/registrations/activation/step_4_acceptance' if @partner.bank_details_added?

https://guides.rubyonrails.org/active_record_validations.html#grouping-conditional-validations