diff --git a/app/controllers/users/dossiers_controller.rb b/app/controllers/users/dossiers_controller.rb
index 88e50718ba1..558c0467a46 100644
--- a/app/controllers/users/dossiers_controller.rb
+++ b/app/controllers/users/dossiers_controller.rb
@@ -128,7 +128,7 @@ def update_identite
       @dossier = dossier
       @no_description = true
 
-      if @dossier.individual.update(individual_params)
+      if @dossier.update(dossier_params)
         @dossier.update!(autorisation_donnees: true, identity_updated_at: Time.zone.now)
         flash.notice = t('.identity_saved')
 
@@ -578,8 +578,8 @@ def render_siret_error(error_message)
       render :siret
     end
 
-    def individual_params
-      params.require(:individual).permit(:gender, :nom, :prenom, :birthdate)
+    def dossier_params
+      params.require(:dossier).permit(:for_tiers, :mandataire_first_name, :mandataire_last_name, individual_attributes: [:gender, :nom, :prenom, :birthdate, :email])
     end
 
     def siret_params
diff --git a/app/javascript/controllers/for_tiers_controller.ts b/app/javascript/controllers/for_tiers_controller.ts
new file mode 100644
index 00000000000..370cc34b71b
--- /dev/null
+++ b/app/javascript/controllers/for_tiers_controller.ts
@@ -0,0 +1,51 @@
+import { ApplicationController } from './application_controller';
+
+export class ForTiersController extends ApplicationController {
+  static values = { procedureid: Number };
+  static targets = [
+    'mandataireFirstName',
+    'mandataireLastName',
+    'forTiers',
+    'mandataireBlock',
+    'beneficiaireNotificationBlock',
+    'email',
+    'notificationMethod'
+  ];
+
+  declare mandataireFirstNameTarget: HTMLInputElement;
+  declare mandataireLastNameTarget: HTMLInputElement;
+  declare forTiersTargets: NodeListOf<HTMLInputElement>;
+  declare mandataireBlockTarget: HTMLElement;
+  declare beneficiaireNotificationBlockTarget: HTMLElement;
+  declare notificationMethodTargets: NodeListOf<HTMLInputElement>;
+  declare emailTarget: HTMLInputElement;
+
+  connect() {
+    this.toggleFieldRequirements();
+    this.addEventListeners();
+  }
+
+  addEventListeners() {
+    this.forTiersTargets.forEach((radio) => {
+      radio.addEventListener('change', () => this.toggleFieldRequirements());
+    });
+  }
+
+  toggleFieldRequirements() {
+    const forTiersSelected = Array.from(this.forTiersTargets).some(
+      (radio) => radio.checked && radio.value === 'true'
+    );
+    this.mandataireBlockTarget.style.display = forTiersSelected
+      ? 'block'
+      : 'none';
+    this.beneficiaireNotificationBlockTarget.style.display = forTiersSelected
+      ? 'block'
+      : 'none';
+    this.mandataireFirstNameTarget.required = forTiersSelected;
+    this.mandataireLastNameTarget.required = forTiersSelected;
+    this.emailTarget.required = forTiersSelected;
+    this.notificationMethodTargets.forEach(
+      (radio) => (radio.required = forTiersSelected)
+    );
+  }
+}