diff --git a/src/app/core/register/register.backend-validators.ts b/src/app/core/register/register.backend-validators.ts
index cdb12ad294..4c1905d93d 100644
--- a/src/app/core/register/register.backend-validators.ts
+++ b/src/app/core/register/register.backend-validators.ts
@@ -61,10 +61,12 @@ export function RegisterBackendValidatorMixin<
       controlName: string,
       value: RegisterForm
     ): Observable<RegisterForm> {
+      // Map validationEndpoint (e.g., 'validatePassword') to endpoint (e.g., 'registerPasswordValidate.json')
+      const endpointSuffix = this.formInputs[controlName].validationEndpoint.replace('validate', '');
       return this._http
         .post<RegisterForm>(
           runtimeEnvironment.API_WEB +
-            `oauth/custom/register/${this.formInputs[controlName].validationEndpoint}.json`,
+            `register${endpointSuffix}Validate.json`,
           value
         )
         .pipe(catchError((error) => this._errorHandler.handleError(error)))
diff --git a/src/app/register/components/form-personal-additional-emails/form-personal-additional-emails.component.html b/src/app/register/components/form-personal-additional-emails/form-personal-additional-emails.component.html
index cae32bc1ee..1333d3995f 100644
--- a/src/app/register/components/form-personal-additional-emails/form-personal-additional-emails.component.html
+++ b/src/app/register/components/form-personal-additional-emails/form-personal-additional-emails.component.html
@@ -42,17 +42,14 @@
     >
       Please enter a valid email address, for example joe&#64;institution.edu
     </mat-error>
-    <ng-container *ngIf="additionalEmailsTouched">
+    <ng-container *ngIf="additionalEmailsTouched || getBackendErrorsForAdditionalEmail(additionalEmailControl.value).length > 0">
       <mat-error
         *ngFor="
-          let error of getControlErrorAtFormLevel(
-            additionalEmailControl.value,
-            'backendErrors'
-          )
+          let error of getBackendErrorsForAdditionalEmail(additionalEmailControl.value)
         "
       >
         <app-backend-error
-          [showEmailAlreadyExistUntilNextButtonWasClicked]="true"
+          [showEmailAlreadyExistUntilNextButtonWasClicked]="false"
           [nextButtonWasClicked]="nextButtonWasClicked"
           [errorCode]="error"
           [value]="additionalEmailControl.value.value"
diff --git a/src/app/register/components/form-personal-additional-emails/form-personal-additional-emails.component.ts b/src/app/register/components/form-personal-additional-emails/form-personal-additional-emails.component.ts
index bce9d17c59..022e553f2d 100644
--- a/src/app/register/components/form-personal-additional-emails/form-personal-additional-emails.component.ts
+++ b/src/app/register/components/form-personal-additional-emails/form-personal-additional-emails.component.ts
@@ -58,6 +58,29 @@ export class FormPersonalAdditionalEmailsComponent implements AfterViewInit {
     )
   }
 
+  // Helper method to safely get backend errors for this email
+  getBackendErrorsForAdditionalEmail(control: AbstractControl | null): string[] {
+    if (!control || !control.parent?.parent?.errors) {
+      return []
+    }
+    
+    const backendErrors = control.parent.parent.errors['backendErrors']
+    if (!backendErrors?.['additionalEmails']) {
+      return []
+    }
+    
+    // Try to match by email value (trim whitespace)
+    const emailValue = control.value?.trim() || ''
+    const errors = backendErrors['additionalEmails'][emailValue]
+    
+    // If not found, try without trimming
+    if (!errors) {
+      return backendErrors['additionalEmails'][control.value] || []
+    }
+    
+    return errors || []
+  }
+
   // deleteEmailInput(id: string): void {
   //   this.additionalEmails.removeControl(id)
   //   this._changeDetectorRef.detectChanges()