diff --git a/examples/getting-started/conversation/send_handle_incoming_sms/server_business_logic.py b/examples/getting-started/conversation/send_handle_incoming_sms/server_business_logic.py
index 6ed9986a..5e9fa615 100644
--- a/examples/getting-started/conversation/send_handle_incoming_sms/server_business_logic.py
+++ b/examples/getting-started/conversation/send_handle_incoming_sms/server_business_logic.py
@@ -34,14 +34,9 @@ def _handle_message_inbound(event: MessageInboundEvent, logger, sinch_client):
     mo_text = _get_mo_text(event)
     logger.info("MO SMS from %s: %s", identity, mo_text)
 
-    app_id = event.app_id
-    if not app_id:
-        logger.warning("Event has no app_id; skipping MT reply.")
-        return
-
     reply_text = f"Your message said: {mo_text}"
     response = sinch_client.conversation.messages.send_text_message(
-        app_id=app_id,
+        app_id=event.app_id,
         text=reply_text,
         recipient_identities=[{"channel": "SMS", "identity": identity}],
     )
diff --git a/sinch/domains/conversation/models/v1/sinch_events/events/conversation_sinch_event_base.py b/sinch/domains/conversation/models/v1/sinch_events/events/conversation_sinch_event_base.py
index 114da8b5..cbd5e50f 100644
--- a/sinch/domains/conversation/models/v1/sinch_events/events/conversation_sinch_event_base.py
+++ b/sinch/domains/conversation/models/v1/sinch_events/events/conversation_sinch_event_base.py
@@ -9,12 +9,10 @@
 class ConversationSinchEventBase(SinchEvent):
     """Base fields present on every Conversation API Sinch Event payload."""
 
-    app_id: Optional[StrictStr] = Field(
-        default=None,
+    app_id: StrictStr = Field(
         description="Id of the subscribed app.",
     )
-    project_id: Optional[StrictStr] = Field(
-        default=None,
+    project_id: StrictStr = Field(
         description="The project ID of the app which has subscribed for the callback.",
     )
     accepted_time: Optional[datetime] = Field(
diff --git a/tests/unit/domains/conversation/v1/models/sinch_events/events/test_conversation_sinch_event_model.py b/tests/unit/domains/conversation/v1/models/sinch_events/events/test_conversation_sinch_event_model.py
index fe5e5c13..f07cb648 100644
--- a/tests/unit/domains/conversation/v1/models/sinch_events/events/test_conversation_sinch_event_model.py
+++ b/tests/unit/domains/conversation/v1/models/sinch_events/events/test_conversation_sinch_event_model.py
@@ -48,6 +48,7 @@ def test_message_delivery_receipt_event_expects_parsed(message_delivery_report_d
 def test_message_inbound_event_expects_parsed():
     payload = {
         "app_id": "app1",
+        "project_id": "proj1",
         "message": {
             "contact_id": "contact1",
             "contact_message": {"text_message": {"text": "Hello"}},
@@ -63,6 +64,7 @@ def test_message_inbound_event_expects_parsed():
 def test_message_submit_event_expects_parsed():
     payload = {
         "app_id": "app1",
+        "project_id": "proj1",
         "message_submit_notification": {
             "contact_id": "contact1",
             "channel_identity": {"channel": "MESSENGER", "identity": "123"},
@@ -73,10 +75,10 @@ def test_message_submit_event_expects_parsed():
     assert event.message_submit_notification.contact_id == "contact1"
 
 
-def test_conversation_sinch_event_base_optional_fields():
-    payload = {"app_id": "app1"}
+def test_conversation_sinch_event_base_optional_timestamp_and_metadata_fields():
+    payload = {"app_id": "app1", "project_id": "proj1"}
     event = ConversationSinchEventBase(**payload)
     assert event.app_id == "app1"
-    assert event.project_id is None
+    assert event.project_id == "proj1"
     assert event.accepted_time is None
     assert event.event_time is None
diff --git a/tests/unit/domains/conversation/v1/sinch_events/test_conversation_sinch_event.py b/tests/unit/domains/conversation/v1/sinch_events/test_conversation_sinch_event.py
index 16d416ca..f9b289fb 100644
--- a/tests/unit/domains/conversation/v1/sinch_events/test_conversation_sinch_event.py
+++ b/tests/unit/domains/conversation/v1/sinch_events/test_conversation_sinch_event.py
@@ -117,7 +117,10 @@ def test_parse_event_message_submit_expects_message_submit_event(conversation_si
 
 
 def test_parse_event_json_string_expects_parsed(conversation_sinch_event):
-    payload_str = '{"app_id":"app1","message_delivery_report":{"status":"DELIVERED"}}'
+    payload_str = (
+        '{"app_id":"app1","project_id":"proj1",'
+        '"message_delivery_report":{"status":"DELIVERED"}}'
+    )
     event = conversation_sinch_event.parse_event(payload_str)
     assert isinstance(event, MessageDeliveryReceiptEvent)
     assert event.app_id == "app1"