diff --git a/yorkie/proto/src/main/proto/yorkie/v1/yorkie.proto b/yorkie/proto/src/main/proto/yorkie/v1/yorkie.proto
index 377b269b8..46e93fd05 100644
--- a/yorkie/proto/src/main/proto/yorkie/v1/yorkie.proto
+++ b/yorkie/proto/src/main/proto/yorkie/v1/yorkie.proto
@@ -48,6 +48,7 @@ message ActivateClientResponse {
 }
 
 message DeactivateClientRequest {
+  string client_key = 2;
   string client_id = 1;
 }
 
@@ -55,6 +56,7 @@ message DeactivateClientResponse {
 }
 
 message AttachDocumentRequest {
+  string client_key = 3;
   string client_id = 1;
   ChangePack change_pack = 2;
 }
@@ -65,6 +67,7 @@ message AttachDocumentResponse {
 }
 
 message DetachDocumentRequest {
+  string client_key = 5;
   string client_id = 1;
   string document_id = 2;
   ChangePack change_pack = 3;
@@ -76,7 +79,9 @@ message DetachDocumentResponse {
 }
 
 message WatchDocumentRequest {
+  string client_key = 4;
   string client_id = 1;
+  string document_key = 3;
   string document_id = 2;
 }
 
@@ -92,6 +97,7 @@ message WatchDocumentResponse {
 }
 
 message RemoveDocumentRequest {
+  string client_key = 4;
   string client_id = 1;
   string document_id = 2;
   ChangePack change_pack = 3;
@@ -102,6 +108,7 @@ message RemoveDocumentResponse {
 }
 
 message PushPullChangesRequest {
+  string client_key = 5;
   string client_id = 1;
   string document_id = 2;
   ChangePack change_pack = 3;
@@ -113,7 +120,9 @@ message PushPullChangesResponse {
 }
 
 message BroadcastRequest {
+  string client_key = 6;
   string client_id = 1;
+  string document_key = 5;
   string document_id = 2;
   string topic = 3;
   bytes payload = 4;
@@ -121,4 +130,3 @@ message BroadcastRequest {
 
 message BroadcastResponse {
 }
-
diff --git a/yorkie/src/androidTest/kotlin/dev/yorkie/document/json/JsonTreeSplitMergeTest.kt b/yorkie/src/androidTest/kotlin/dev/yorkie/document/json/JsonTreeSplitMergeTest.kt
index 9c68bde9e..cbc20773d 100644
--- a/yorkie/src/androidTest/kotlin/dev/yorkie/document/json/JsonTreeSplitMergeTest.kt
+++ b/yorkie/src/androidTest/kotlin/dev/yorkie/document/json/JsonTreeSplitMergeTest.kt
@@ -244,7 +244,7 @@ class JsonTreeSplitMergeTest {
     }
 
     @Test
-    fun test_split_and_merge_with_empty_paragraph_left_and_multiple_split_level_left() {
+    fun test_split_and_merge_with_empty_paragraph_and_multiple_split_level_left() {
         withTwoClientsAndDocuments(realTimeSync = false) { c1, c2, d1, d2, _ ->
             d1.updateAsync { root, _ ->
                 root.setNewTree(
diff --git a/yorkie/src/main/kotlin/dev/yorkie/core/Client.kt b/yorkie/src/main/kotlin/dev/yorkie/core/Client.kt
index c4d01d25b..35413ccb5 100644
--- a/yorkie/src/main/kotlin/dev/yorkie/core/Client.kt
+++ b/yorkie/src/main/kotlin/dev/yorkie/core/Client.kt
@@ -207,6 +207,7 @@ public class Client @VisibleForTesting internal constructor(
                             changePack = document.createChangePack().toPBChangePack()
                             documentId = documentID
                             pushOnly = syncMode == SyncMode.PushOnly
+                            clientKey = options.key
                         }
                         val response = service.pushPullChanges(
                             request,
@@ -257,6 +258,8 @@ public class Client @VisibleForTesting internal constructor(
                 watchDocumentRequest {
                     clientId = requireClientId().value
                     documentId = attachment.documentID
+                    clientKey = options.key
+                    documentKey = attachment.document.key.value
                 },
                 documentBasedRequestHeader(attachment.document.key),
             ).retry {
@@ -350,6 +353,7 @@ public class Client @VisibleForTesting internal constructor(
             val request = attachDocumentRequest {
                 clientId = requireClientId().value
                 changePack = document.createChangePack().toPBChangePack()
+                clientKey = options.key
             }
             val response = try {
                 service.attachDocument(
@@ -402,6 +406,7 @@ public class Client @VisibleForTesting internal constructor(
                 clientId = requireClientId().value
                 changePack = document.createChangePack().toPBChangePack()
                 documentId = attachment.documentID
+                clientKey = options.key
             }
             val response = try {
                 service.detachDocument(
@@ -437,6 +442,7 @@ public class Client @VisibleForTesting internal constructor(
                 service.deactivateClient(
                     deactivateClientRequest {
                         clientId = requireClientId().value
+                        clientKey = options.key
                     },
                     projectBasedRequestHeader,
                 )
@@ -464,6 +470,7 @@ public class Client @VisibleForTesting internal constructor(
                 clientId = requireClientId().value
                 changePack = document.createChangePack(forceRemove = true).toPBChangePack()
                 documentId = attachment.documentID
+                clientKey = options.key
             }
             val response = try {
                 service.removeDocument(