Fix bug and add unit test

src/registrar/admin.py

@@ -1846,7 +1846,7 @@ class PortfolioInvitationAdmin(BaseInvitationAdmin):
                 requested_user = get_requested_user(requested_email)
 
                 permission_exists = UserPortfolioPermission.objects.filter(
-                    user__email=requested_email, portfolio=portfolio, user__email__isnull=False
+                    user__email__iexact=requested_email, portfolio=portfolio, user__email__isnull=False
                 ).exists()
                 if not permission_exists:
                     # if permission does not exist for a user with requested_email, send email
@@ -1857,7 +1857,7 @@ class PortfolioInvitationAdmin(BaseInvitationAdmin):
                         is_admin_invitation=is_admin_invitation,
                     ):
                         messages.warning(
-                            self.request, "Could not send email notification to existing organization admins."
+                            request, "Could not send email notification to existing organization admins."
                         )
                     # if user exists for email, immediately retrieve portfolio invitation upon creation
                     if requested_user is not None:

src/registrar/tests/test_views_portfolio.py

@@ -3952,6 +3952,46 @@ class TestPortfolioInviteNewMemberView(MockEppLib, WebTest):
         # assert that send_portfolio_invitation_email is not called
         mock_send_email.assert_not_called()
 
+    @less_console_noise_decorator
+    @override_flag("organization_feature", active=True)
+    @override_flag("organization_members", active=True)
+    @patch("registrar.views.portfolios.send_portfolio_invitation_email")
+    def test_member_invite_for_existing_member_uppercase(self, mock_send_email):
+        """Tests the member invitation flow for existing portfolio member with a different case."""
+        self.client.force_login(self.user)
+
+        # Simulate a session to ensure continuity
+        session_id = self.client.session.session_key
+        self.app.set_cookie(settings.SESSION_COOKIE_NAME, session_id)
+
+        invite_count_before = PortfolioInvitation.objects.count()
+
+        # Simulate submission of member invite for user who has already been invited
+        response = self.client.post(
+            reverse("new-member"),
+            {
+                "role": UserPortfolioRoleChoices.ORGANIZATION_ADMIN,
+                "email": self.user.email.upper(),
+            },
+            follow=True,
+        )
+        self.assertEqual(response.status_code, 200)
+        with open("debug_response.html", "w") as f:
+            f.write(response.content.decode("utf-8"))
+
+        # Verify messages
+        self.assertContains(
+            response,
+            "User is already a member of this portfolio.",
+        )
+
+        # Validate Database has not changed
+        invite_count_after = PortfolioInvitation.objects.count()
+        self.assertEqual(invite_count_after, invite_count_before)
+
+        # assert that send_portfolio_invitation_email is not called
+        mock_send_email.assert_not_called()
+
     @less_console_noise_decorator
     @override_flag("organization_feature", active=True)
     @override_flag("organization_members", active=True)

src/registrar/views/portfolios.py

@@ -970,7 +970,7 @@ class PortfolioAddMemberView(DetailView, FormMixin):
         portfolio = form.cleaned_data["portfolio"]
         is_admin_invitation = UserPortfolioRoleChoices.ORGANIZATION_ADMIN in form.cleaned_data["roles"]
 
-        requested_user = User.objects.filter(email=requested_email).first()
+        requested_user = User.objects.filter(email__iexact=requested_email).first()
         permission_exists = UserPortfolioPermission.objects.filter(user=requested_user, portfolio=portfolio).exists()
         try:
             if not requested_user or not permission_exists: