diff --git a/engine/apps/api/errors.py b/engine/apps/api/errors.py
new file mode 100644
index 00000000..3c43686a
--- /dev/null
+++ b/engine/apps/api/errors.py
@@ -0,0 +1,18 @@
+"""errors contains business-logic error codes for internal api.
+
+It's expected that error codes will use 1000-9999 codes range, where first two digits are for entity:
+11xx - AlertGroup, 12xx - AlertReceiveChannel, etc.
+10xx are saved for non-entity related errors.
+"""
+# TODO: this package is WIP. It requires validation of code ranges.
+from enum import Enum, unique
+
+
+@unique
+class AlertGroupAPIError(Enum):
+    """
+    Error codes for alert group.
+    Range is 1100-1199
+    """
+
+    RESOLUTION_NOTE_REQUIRED = 1101
diff --git a/engine/apps/api/tests/test_alert_group.py b/engine/apps/api/tests/test_alert_group.py
index e8a8e2ac..ea815f28 100644
--- a/engine/apps/api/tests/test_alert_group.py
+++ b/engine/apps/api/tests/test_alert_group.py
@@ -9,6 +9,7 @@ from rest_framework.response import Response
 from rest_framework.test import APIClient
 
 from apps.alerts.models import AlertGroup, AlertGroupLogRecord, AlertReceiveChannel
+from apps.api.errors import AlertGroupAPIError
 from apps.api.permissions import LegacyAccessControlRole
 from apps.base.models import UserNotificationPolicyLogRecord
 
@@ -1805,3 +1806,42 @@ def test_direct_paging_integration_treated_as_deleted(
 
     response = client.get(url, format="json", **make_user_auth_headers(user, token))
     assert response.json()["alert_receive_channel"]["deleted"] is True
+
+
+@pytest.mark.django_db
+def test_alert_group_resolve_resolution_note(
+    make_organization_and_user_with_plugin_token,
+    make_alert_receive_channel,
+    make_channel_filter,
+    make_alert_group,
+    make_alert,
+    make_user_auth_headers,
+):
+    organization, user, token = make_organization_and_user_with_plugin_token()
+    alert_receive_channel = make_alert_receive_channel(organization)
+    channel_filter = make_channel_filter(alert_receive_channel, is_default=True)
+    new_alert_group = make_alert_group(alert_receive_channel, channel_filter=channel_filter)
+    make_alert(alert_group=new_alert_group, raw_request_data=alert_raw_request_data)
+
+    organization.is_resolution_note_required = True
+    organization.save()
+
+    client = APIClient()
+    url = reverse("api-internal:alertgroup-resolve", kwargs={"pk": new_alert_group.public_primary_key})
+
+    response = client.post(url, format="json", **make_user_auth_headers(user, token))
+    # check that resolution note is required
+    assert response.status_code == status.HTTP_400_BAD_REQUEST
+    assert response.json()["code"] == AlertGroupAPIError.RESOLUTION_NOTE_REQUIRED.value
+
+    with patch(
+        "apps.alerts.tasks.send_update_resolution_note_signal.send_update_resolution_note_signal.apply_async"
+    ) as mock_signal:
+        url = reverse("api-internal:alertgroup-resolve", kwargs={"pk": new_alert_group.public_primary_key})
+        response = client.post(
+            url, format="json", data={"resolution_note": "hi"}, **make_user_auth_headers(user, token)
+        )
+        assert response.status_code == status.HTTP_200_OK
+
+        assert new_alert_group.has_resolution_notes
+        assert mock_signal.called
diff --git a/engine/apps/api/views/alert_group.py b/engine/apps/api/views/alert_group.py
index 4442e8dd..bcae5306 100644
--- a/engine/apps/api/views/alert_group.py
+++ b/engine/apps/api/views/alert_group.py
@@ -13,8 +13,10 @@ from rest_framework.permissions import IsAuthenticated
 from rest_framework.response import Response
 
 from apps.alerts.constants import ActionSource
-from apps.alerts.models import Alert, AlertGroup, AlertReceiveChannel, EscalationChain
+from apps.alerts.models import Alert, AlertGroup, AlertReceiveChannel, EscalationChain, ResolutionNote
 from apps.alerts.paging import unpage_user
+from apps.alerts.tasks import send_update_resolution_note_signal
+from apps.api.errors import AlertGroupAPIError
 from apps.api.permissions import RBACPermission
 from apps.api.serializers.alert_group import AlertGroupListSerializer, AlertGroupSerializer
 from apps.api.serializers.team import TeamSerializer
@@ -456,11 +458,30 @@ class AlertGroupView(
         if alert_group.is_maintenance_incident:
             alert_group.stop_maintenance(self.request.user)
         else:
-            if organization.is_resolution_note_required and not alert_group.has_resolution_notes:
-                return Response(
-                    data="Alert group without resolution note cannot be resolved due to organization settings.",
-                    status=status.HTTP_400_BAD_REQUEST,
+            resolution_note_text = request.data.get("resolution_note")
+            if resolution_note_text:
+                rn = ResolutionNote.objects.create(
+                    alert_group=alert_group,
+                    author=self.request.user,
+                    source=ResolutionNote.Source.WEB,
+                    message_text=resolution_note_text[:3000],  # trim text to fit in the db field
                 )
+                send_update_resolution_note_signal.apply_async(
+                    kwargs={
+                        "alert_group_pk": alert_group.pk,
+                        "resolution_note_pk": rn.pk,
+                    }
+                )
+            else:
+                # Check resolution note required setting only if resolution_note_text was not provided.
+                if organization.is_resolution_note_required and not alert_group.has_resolution_notes:
+                    return Response(
+                        data={
+                            "code": AlertGroupAPIError.RESOLUTION_NOTE_REQUIRED.value,
+                            "detail": "Alert group without resolution note cannot be resolved due to organization settings",
+                        },
+                        status=status.HTTP_400_BAD_REQUEST,
+                    )
             alert_group.resolve_by_user(self.request.user, action_source=ActionSource.WEB)
         return Response(AlertGroupSerializer(alert_group, context={"request": self.request}).data)