improve multiple submitters error message

app/controllers/start_form_controller.rb

@@ -25,7 +25,7 @@ class StartFormController < ApplicationController
       redirect_to start_form_completed_path(@template.slug, email: submitter_params[:email])
     else
       if filter_undefined_submitters(@template).size > 1 && @submitter.new_record?
-        @error_message = I18n.t('not_found')
+        @error_message = multiple_submitters_error_message
 
         return render :show
       end
@@ -117,4 +117,14 @@ class StartFormController < ApplicationController
 
     @template = Template.find_by!(slug:)
   end
+
+  # rubocop:disable Layout/LineLength
+  def multiple_submitters_error_message
+    if current_user&.account_id == @template.account_id
+      helpers.t('this_submission_has_multiple_signers_which_prevents_the_use_of_a_sharing_link_as_its_unclear_which_signer_is_responsible_for_specific_fields_to_resolve_this_follow_this_guide_to_define_the_default_signer_details_html')
+    else
+      I18n.t('not_found')
+    end
+  end
+  # rubocop:enable Layout/LineLength
 end

app/views/start_form/show.html.erb

@@ -30,7 +30,9 @@
         <div dir="auto" class="form-control !mt-0">
           <%= f.label :email, t('email'), class: 'label' %>
           <%= f.email_field :email, value: current_user&.email || params[:email] || @submitter.email, required: true, class: 'base-input', placeholder: t('provide_your_email_to_start') %>
-          <%= @error_message %>
+          <% if @error_message %>
+            <span class="label-text-alt text-red-400 mt-1"><%= @error_message %></span>
+          <% end %>
         </div>
         <toggle-submit dir="auto" class="form-control">
           <%= f.button button_title(title: t('start'), disabled_with: t('starting')), class: 'base-button' %>

config/locales/i18n.yml

@@ -700,6 +700,7 @@ en: &en
   submission_created_via_source_html: '<b>Submission created</b> via %{source}'
   pro_user_seats_used: Pro user seats used
   manage_plan: Manage plan
+  this_submission_has_multiple_signers_which_prevents_the_use_of_a_sharing_link_as_its_unclear_which_signer_is_responsible_for_specific_fields_to_resolve_this_follow_this_guide_to_define_the_default_signer_details_html: This submission has multiple signers, which prevents the use of a sharing link as it's unclear which signer is responsible for specific fields. To resolve this, follow this <a href="https://www.docuseal.com/resources/pre-filling-recipients" class="link font-bold" rel="noopener noreferrer nofollow" target="_blank">guide</a> to define the default signer details.
   submission_sources:
     api: API
     bulk: Bulk Send
@@ -1426,6 +1427,7 @@ es: &es
   submission_created_via_source_html: '<b>Envío creado</b> a través de %{source}'
   pro_user_seats_used: Plazas de usuario Pro en uso
   manage_plan: Gestionar plan
+  this_submission_has_multiple_signers_which_prevents_the_use_of_a_sharing_link_as_its_unclear_which_signer_is_responsible_for_specific_fields_to_resolve_this_follow_this_guide_to_define_the_default_signer_details_html: 'Este envío tiene múltiples firmantes, lo que impide el uso de un enlace para compartir, ya que no está claro qué firmante es responsable de los campos específicos. Para resolver esto, sigue esta <a href="https://www.docuseal.com/resources/pre-filling-recipients" class="link font-bold" rel="noopener noreferrer nofollow" target="_blank">guía</a> para definir los detalles predeterminados del firmante.'
   submission_sources:
     api: API
     bulk: Envío masivo
@@ -2151,6 +2153,7 @@ it: &it
   submission_created_via_source_html: '<b>Invio creato</b> tramite %{source}'
   pro_user_seats_used: Posti utente Pro in uso
   manage_plan: Gestisci piano
+  this_submission_has_multiple_signers_which_prevents_the_use_of_a_sharing_link_as_its_unclear_which_signer_is_responsible_for_specific_fields_to_resolve_this_follow_this_guide_to_define_the_default_signer_details_html: "Questa sottomissione ha più firmatari, il che impedisce l'uso di un link di condivisione poiché non è chiaro quale firmatario sia responsabile di specifici campi. Per risolvere questo problema, segui questa <a href=\"https://www.docuseal.com/resources/pre-filling-recipients\" class=\"link font-bold\" rel=\"noopener noreferrer nofollow\" target=\"_blank\">guida</a> per definire i dettagli predefiniti del firmatario."
   submission_sources:
     api: API
     bulk: Invio massivo
@@ -2878,6 +2881,7 @@ fr: &fr
   submission_created_via_source_html: '<b>Soumission créée</b> via %{source}'
   pro_user_seats_used: Places utilisateur Pro en cours d'utilisation
   manage_plan: Gérer le plan
+  this_submission_has_multiple_signers_which_prevents_the_use_of_a_sharing_link_as_its_unclear_which_signer_is_responsible_for_specific_fields_to_resolve_this_follow_this_guide_to_define_the_default_signer_details_html: 'Cette soumission comporte plusieurs signataires, ce qui empêche l’utilisation d’un lien de partage, car il n’est pas clair quel signataire est responsable de quels champs. Pour résoudre ce problème, suivez ce <a href="https://www.docuseal.com/resources/pre-filling-recipients" class="link font-bold" rel="noopener noreferrer nofollow" target="_blank">guide</a> pour définir les détails du signataire par défaut.'
   submission_sources:
     api: API
     bulk: Envoi en masse
@@ -3604,6 +3608,7 @@ pt: &pt
   submission_created_via_source_html: '<b>Envio criado</b> via %{source}'
   pro_user_seats_used: Lugares de usuário Pro em uso
   manage_plan: Gerenciar plano
+  this_submission_has_multiple_signers_which_prevents_the_use_of_a_sharing_link_as_its_unclear_which_signer_is_responsible_for_specific_fields_to_resolve_this_follow_this_guide_to_define_the_default_signer_details_html: 'Este envio tem vários signatários, o que impede o uso de um link de compartilhamento, pois não está claro qual signatário é responsável por quais campos. Para resolver isso, siga este <a href="https://www.docuseal.com/resources/pre-filling-recipients" class="link font-bold" rel="noopener noreferrer nofollow" target="_blank">guia</a> para definir os detalhes padrão do signatário.'
   submission_sources:
     api: API
     bulk: Envio em massa
@@ -4330,6 +4335,7 @@ de: &de
   submission_created_via_source_html: '<b>Übermittlung erstellt</b> über %{source}'
   pro_user_seats_used: Verwendete Pro-Benutzerplätze
   manage_plan: Plan verwalten
+  this_submission_has_multiple_signers_which_prevents_the_use_of_a_sharing_link_as_its_unclear_which_signer_is_responsible_for_specific_fields_to_resolve_this_follow_this_guide_to_define_the_default_signer_details_html: 'Diese Übermittlung hat mehrere Unterzeichner, was die Nutzung eines Freigabelinks verhindert, da unklar ist, welcher Unterzeichner für welche Felder verantwortlich ist. Um dies zu lösen, folgen Sie dieser <a href="https://www.docuseal.com/resources/pre-filling-recipients" class="link font-bold" rel="noopener noreferrer nofollow" target="_blank">Anleitung</a>, um die Standarddetails des Unterzeichners festzulegen.'
   submission_sources:
     api: API
     bulk: Massenversand

spec/system/signing_form_spec.rb

@@ -796,6 +796,40 @@ RSpec.describe 'Signing Form', type: :system do
     end
   end
 
+  context 'when the template requires multiple submitters' do
+    let(:template) { create(:template, submitter_count: 2, account:, author:, only_field_types: %w[text]) }
+
+    context 'when default signer details are not defined' do
+      it 'shows an explanation error message if a logged-in user associated with the template account opens the link' do
+        sign_in author
+        visit start_form_path(slug: template.slug)
+        fill_in 'Email', with: author.email
+        click_button 'Start'
+
+        expect(page).to have_content('This submission has multiple signers, which prevents the use of a sharing link ' \
+                                     "as it's unclear which signer is responsible for specific fields. " \
+                                     'To resolve this, follow this guide to define the default signer details.')
+        expect(page).to have_link('guide', href: 'https://www.docuseal.com/resources/pre-filling-recipients')
+      end
+
+      it 'shows a "Not found" error message if a logged-out user associated with the template account opens the link' do
+        visit start_form_path(slug: template.slug)
+        fill_in 'Email', with: author.email
+        click_button 'Start'
+
+        expect(page).to have_content('Not found')
+      end
+
+      it 'shows a "Not found" error message if an unrelated user opens the link' do
+        visit start_form_path(slug: template.slug)
+        fill_in 'Email', with: 'john.doe@example.com'
+        click_button 'Start'
+
+        expect(page).to have_content('Not found')
+      end
+    end
+  end
+
   it 'sends completed email' do
     template = create(:template, account:, author:, only_field_types: %w[text signature])
     submission = create(:submission, template:)