diff --git a/checkout_sdk/accounts/accounts.py b/checkout_sdk/accounts/accounts.py
index e2d1ae77..5225b14d 100644
--- a/checkout_sdk/accounts/accounts.py
+++ b/checkout_sdk/accounts/accounts.py
@@ -520,11 +520,15 @@ def __init__(self, frequency_p: ScheduleFrequency):
 
 
 class ScheduleFrequencyDailyRequest(ScheduleRequest):
+    # For ISV (SaaS seller) sub-entities, a daily schedule runs on working days only
+    # (Monday to Friday); payouts do not take place on weekends.
     def __init__(self):
         super().__init__(ScheduleFrequency.DAILY)
 
 
 class ScheduleFrequencyMonthlyRequest(ScheduleRequest):
+    # For ISV (SaaS seller) sub-entities, by_month_day accepts only the combinations
+    # [1], [15], [1, 15] or [1, 16], in any order.
     by_month_day: list  # int
 
     def __init__(self):
@@ -532,6 +536,8 @@ def __init__(self):
 
 
 class ScheduleFrequencyWeeklyRequest(ScheduleRequest):
+    # For ISV (SaaS seller) sub-entities, by_day accepts working days only
+    # (Monday to Friday); payouts set to take place on weekends are rejected.
     by_day: list  # DaySchedule
 
     def __init__(self):
@@ -541,6 +547,14 @@ def __init__(self):
 class UpdateScheduleRequest:
     enabled: bool
     threshold: int
+    # The amount, in the minor units of the schedule's currency, to retain in the
+    # sub-entity's available balance. ISV (SaaS seller) sub-entities only. Min 0.
+    balance_minimum: int
+    # Indicates whether to carry forward any balance below the configured minimum
+    # to the next payout. ISV (SaaS seller) sub-entities only.
+    carry_forward_enabled: bool
+    # The ID of the platforms payment instrument used as the payout destination.
+    payment_instrument_id: str
     recurrence: ScheduleRequest
 
 
diff --git a/tests/accounts/update_schedule_request_serialization_test.py b/tests/accounts/update_schedule_request_serialization_test.py
new file mode 100644
index 00000000..d9fd05cf
--- /dev/null
+++ b/tests/accounts/update_schedule_request_serialization_test.py
@@ -0,0 +1,47 @@
+import json
+
+from checkout_sdk.json_serializer import JsonSerializer
+from checkout_sdk.accounts.accounts import (
+    DaySchedule, ScheduleFrequencyWeeklyRequest, UpdateScheduleRequest,
+)
+
+
+def _serialize(obj):
+    return json.loads(json.dumps(obj, cls=JsonSerializer))
+
+
+class TestUpdateScheduleRequestSerialization:
+
+    def test_serializes_isv_fields_when_set(self):
+        recurrence = ScheduleFrequencyWeeklyRequest()
+        recurrence.by_day = [DaySchedule.MONDAY]
+
+        request = UpdateScheduleRequest()
+        request.enabled = True
+        request.threshold = 100
+        request.balance_minimum = 500
+        request.carry_forward_enabled = True
+        request.payment_instrument_id = 'ppi_w4jelhppmfiufdnatam37wrfc4'
+        request.recurrence = recurrence
+
+        assert _serialize(request) == {
+            'enabled': True,
+            'threshold': 100,
+            'balance_minimum': 500,
+            'carry_forward_enabled': True,
+            'payment_instrument_id': 'ppi_w4jelhppmfiufdnatam37wrfc4',
+            'recurrence': {
+                'frequency': 'weekly',
+                'by_day': ['monday'],
+            },
+        }
+
+    def test_omits_isv_fields_when_unset(self):
+        request = UpdateScheduleRequest()
+        request.enabled = False
+
+        serialized = _serialize(request)
+        assert serialized == {'enabled': False}
+        assert 'balance_minimum' not in serialized
+        assert 'carry_forward_enabled' not in serialized
+        assert 'payment_instrument_id' not in serialized