diff --git a/.idea/Rasaddam_Backend.iml b/.idea/Rasaddam_Backend.iml
index c5d6090..168bde0 100644
--- a/.idea/Rasaddam_Backend.iml
+++ b/.idea/Rasaddam_Backend.iml
@@ -14,7 +14,7 @@
   </component>
   <component name="NewModuleRootManager">
     <content url="file://$MODULE_DIR$" />
-    <orderEntry type="jdk" jdkName="Python 3.10 (bazrasienv)" jdkType="Python SDK" />
+    <orderEntry type="jdk" jdkName="Python 3.10 (env)" jdkType="Python SDK" />
     <orderEntry type="sourceFolder" forTests="false" />
   </component>
   <component name="PyDocumentationSettings">
diff --git a/.idea/misc.xml b/.idea/misc.xml
index 29f5506..296aa57 100644
--- a/.idea/misc.xml
+++ b/.idea/misc.xml
@@ -1,4 +1,4 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
-  <component name="ProjectRootManager" version="2" project-jdk-name="Python 3.10 (bazrasienv)" project-jdk-type="Python SDK" />
+  <component name="ProjectRootManager" version="2" project-jdk-name="Python 3.10 (env)" project-jdk-type="Python SDK" />
 </project>
\ No newline at end of file
diff --git a/apps/authentication/api/v1/api.py b/apps/authentication/api/v1/api.py
index 7192d70..f0726c2 100644
--- a/apps/authentication/api/v1/api.py
+++ b/apps/authentication/api/v1/api.py
@@ -300,12 +300,6 @@ class OrganizationViewSet(ModelViewSet, DynamicSearchMixin):
         else:
             queryset = self.queryset.filter(province=request.user.province)
 
-        # if param self was in request, remove my organization from queryset
-        if 'self' in request.GET.keys():
-            queryset = self.queryset.filter(
-                province=int(request.GET['province'])
-            ).exclude(user_organization__user=request.user)
-
         filtered_query = self.filter_query(queryset)
 
         page = self.paginate_queryset(filtered_query.order_by('-create_date'))  # paginate queryset
diff --git a/apps/pos_device/exceptions.py b/apps/pos_device/exceptions.py
new file mode 100644
index 0000000..a2e926c
--- /dev/null
+++ b/apps/pos_device/exceptions.py
@@ -0,0 +1,7 @@
+from rest_framework.exceptions import APIException
+from rest_framework import status
+
+
+class DeviceAlreadyAssigned(APIException):
+    status_code = status.HTTP_403_FORBIDDEN
+    default_detail = "این دستگاه قبلا به این کلاینت تخصیص داده شده است"  # noqa
diff --git a/apps/pos_device/migrations/0055_alter_posclient_organization_and_more.py b/apps/pos_device/migrations/0055_alter_posclient_organization_and_more.py
new file mode 100644
index 0000000..a4d73ff
--- /dev/null
+++ b/apps/pos_device/migrations/0055_alter_posclient_organization_and_more.py
@@ -0,0 +1,26 @@
+# Generated by Django 5.0 on 2025-08-16 10:08
+
+import django.db.models.deletion
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('authentication', '0033_organization_en_name_alter_organization_name'),
+        ('pos_device', '0054_alter_deviceactivationcode_expires_at'),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='posclient',
+            name='organization',
+            field=models.ForeignKey(null=True, on_delete=django.db.models.deletion.CASCADE, related_name='client', to='authentication.organization'),
+        ),
+        migrations.AddConstraint(
+            model_name='deviceassignment',
+            constraint=models.UniqueConstraint(fields=('client', 'device'), name='unique_assign_client_device', violation_error_code=403, violation_error_message='این کلاینت با همین دستگاه قبلا تخصیص داده شده است'),
+        ),
+    ]
diff --git a/apps/pos_device/migrations/0056_remove_deviceassignment_unique_assign_client_device.py b/apps/pos_device/migrations/0056_remove_deviceassignment_unique_assign_client_device.py
new file mode 100644
index 0000000..5104aef
--- /dev/null
+++ b/apps/pos_device/migrations/0056_remove_deviceassignment_unique_assign_client_device.py
@@ -0,0 +1,17 @@
+# Generated by Django 5.0 on 2025-08-16 10:50
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('pos_device', '0055_alter_posclient_organization_and_more'),
+    ]
+
+    operations = [
+        migrations.RemoveConstraint(
+            model_name='deviceassignment',
+            name='unique_assign_client_device',
+        ),
+    ]
diff --git a/apps/pos_device/models.py b/apps/pos_device/models.py
index c6d8ca9..b6cdb68 100644
--- a/apps/pos_device/models.py
+++ b/apps/pos_device/models.py
@@ -148,7 +148,7 @@ class POSClient(BaseModel):
         ('organization', 'سازمان')  # noqa
     ])
     is_organization = models.BooleanField(default=False)
-    organization = models.OneToOneField(
+    organization = models.ForeignKey(
         Organization,
         on_delete=models.CASCADE,
         related_name='client',
diff --git a/apps/pos_device/web/api/v1/serilaizers/client.py b/apps/pos_device/web/api/v1/serilaizers/client.py
index 83e625d..cce4aa6 100644
--- a/apps/pos_device/web/api/v1/serilaizers/client.py
+++ b/apps/pos_device/web/api/v1/serilaizers/client.py
@@ -1,5 +1,7 @@
 from rest_framework.serializers import ModelSerializer
 from apps.pos_device import models as pos_models
+from rest_framework.exceptions import APIException
+from rest_framework import status
 
 
 class POSClientSerializer(ModelSerializer):
@@ -7,6 +9,26 @@ class POSClientSerializer(ModelSerializer):
         model = pos_models.POSClient
         fields = '__all__'
 
+    def validate(self, attrs):
+        org = attrs['organization']
+
+        # check for duplicate organization client
+        if org:
+            if self.Meta.model.objects.filter(organization=org).exists():
+                raise APIException("قبلا کلاینت با این سازمان ثبت شده است", code=status.HTTP_403_FORBIDDEN)  # noqa
+
+        return attrs
+
+    def to_representation(self, instance):
+        representation = super().to_representation(instance)
+
+        representation['organization'] = {
+            'name': instance.organization.name,
+            'id': instance.organization.id
+        }
+
+        return representation
+
 
 class POSClientAttributeSerializer(ModelSerializer):
     class Meta:
diff --git a/apps/pos_device/web/api/v1/serilaizers/device.py b/apps/pos_device/web/api/v1/serilaizers/device.py
index f067e66..826c312 100644
--- a/apps/pos_device/web/api/v1/serilaizers/device.py
+++ b/apps/pos_device/web/api/v1/serilaizers/device.py
@@ -1,5 +1,9 @@
+from apps.pos_device.web.api.v1.serilaizers import client as client_serializer
 from rest_framework.serializers import ModelSerializer
 from apps.pos_device import models as pos_models
+from rest_framework.exceptions import APIException
+from apps.pos_device import exceptions as pos_exceptions
+from rest_framework import status
 
 
 class ProviderCompanySerializer(ModelSerializer):
@@ -23,6 +27,10 @@ class DeviceSerializer(ModelSerializer):
             'province': instance.organization.province.id
         }
 
+        representation['assignment'] = DeviceAssignmentSerializer(
+            instance.assignment.all().first()
+        ).data
+
         return representation
 
 
@@ -43,6 +51,23 @@ class DeviceAssignmentSerializer(ModelSerializer):
         model = pos_models.DeviceAssignment
         fields = '__all__'
 
+    def validate(self, attrs):
+
+        device = attrs['device']
+        client = attrs['client']
+
+        if self.Meta.model.objects.filter(device=device, client=client).exists():
+            raise pos_exceptions.DeviceAlreadyAssigned()
+
+    def to_representation(self, instance):
+        representation = super().to_representation(instance)
+
+        representation['client'] = client_serializer.POSClientSerializer(
+            instance.client
+        ).data
+
+        return representation
+
 
 class StakeHoldersSerializer(ModelSerializer):
     class Meta:
diff --git a/apps/pos_device/web/api/v1/viewsets/device.py b/apps/pos_device/web/api/v1/viewsets/device.py
index 77045ea..17c2dec 100644
--- a/apps/pos_device/web/api/v1/viewsets/device.py
+++ b/apps/pos_device/web/api/v1/viewsets/device.py
@@ -164,15 +164,8 @@ class DeviceAssignmentViewSet(viewsets.ModelViewSet):
     queryset = pos_models.DeviceAssignment.objects.all()
     serializer_class = device_serializer.DeviceAssignmentSerializer
 
-    @action(
-        methods=['post'],
-        detail=False,
-        url_path='assignment',
-        url_name='assignment',
-        name='assignment',
-    )
     @transaction.atomic
-    def device_assignment(self, request):
+    def create(self, request, *args, **kwargs):
         """ assign pos device to client by company """
 
         if 'organization' not in request.data.keys():
@@ -180,12 +173,22 @@ class DeviceAssignmentViewSet(viewsets.ModelViewSet):
             request.data.update({'organization': organization.id})
 
         if 'client_data' in request.data.keys():
-            client = CustomOperations().custom_create(
-                request=request,
-                view=POSClientViewSet(),
-                data=request.data['client_data']
-            )
-            request.data.update({'client': client['id']})
+
+            # if client will be an organization
+            if request.data['client_data']['is_organization']:
+                client = pos_models.POSClient.objects.filter(
+                        organization_id=request.data['client_data']['organization']
+                )
+
+                if client.exists():
+                    request.data.update({'client': client.first().id})
+            else:
+                client = CustomOperations().custom_create(
+                    request=request,
+                    view=POSClientViewSet(),
+                    data=request.data['client_data']
+                )
+                request.data.update({'client': client['id']})
 
         # create assignment
         serializer = self.serializer_class(data=request.data)
@@ -193,8 +196,9 @@ class DeviceAssignmentViewSet(viewsets.ModelViewSet):
             assignment = serializer.save()
 
             # set organization having pos status
-            assignment.organization.has_pos = True
-            assignment.organization.save()
+            if assignment.client.organization:
+                assignment.client.organization.has_pos = True
+                assignment.client.organization.save()
 
             return Response(serializer.data, status=status.HTTP_201_CREATED)
         return Response(serializer.errors, status=status.HTTP_403_FORBIDDEN)