diff --git a/SeatsioDotNet.Test/HoldTokens/RetrieveHoldTokenTest.cs b/SeatsioDotNet.Test/HoldTokens/RetrieveHoldTokenTest.cs
index 50b0673..81a6095 100644
--- a/SeatsioDotNet.Test/HoldTokens/RetrieveHoldTokenTest.cs
+++ b/SeatsioDotNet.Test/HoldTokens/RetrieveHoldTokenTest.cs
@@ -14,7 +14,7 @@ public void Test()
             Assert.Equal(holdToken.Token, retrievedHoldToken.Token);
             Assert.Equal(holdToken.ExpiresAt, retrievedHoldToken.ExpiresAt);
             Assert.InRange(holdToken.ExpiresInSeconds, 14 * 60, 15 * 60);
-            Assert.True(holdToken.AccountId > 0);
+            Assert.NotNull(holdToken.workspaceKey);
         }
     }
 }
\ No newline at end of file
diff --git a/SeatsioDotNet.Test/SeatsioClientTest.cs b/SeatsioDotNet.Test/SeatsioClientTest.cs
index d29065a..c2bd2da 100644
--- a/SeatsioDotNet.Test/SeatsioClientTest.cs
+++ b/SeatsioDotNet.Test/SeatsioClientTest.cs
@@ -67,9 +67,9 @@ protected SeatsioClient CreateSeatsioClient(string secretKey)
             return new SeatsioClient(secretKey, null, BaseUrl);
         }
 
-        protected SeatsioClient CreateSeatsioClient(string secretKey, long accountId)
+        protected SeatsioClient CreateSeatsioClient(string secretKey, string workspaceKey)
         {
-            return new SeatsioClient(secretKey, accountId, BaseUrl);
+            return new SeatsioClient(secretKey, workspaceKey, BaseUrl);
         }
     }
 }
\ No newline at end of file
diff --git a/SeatsioDotNet.Test/Subaccounts/RetrieveSubaccountTest.cs b/SeatsioDotNet.Test/Subaccounts/RetrieveSubaccountTest.cs
index fb37706..96b6c52 100644
--- a/SeatsioDotNet.Test/Subaccounts/RetrieveSubaccountTest.cs
+++ b/SeatsioDotNet.Test/Subaccounts/RetrieveSubaccountTest.cs
@@ -17,7 +17,7 @@ public void Test()
             Assert.Equal(subaccount.PublicKey, retrievedSubaccount.PublicKey);
             Assert.Equal("joske", retrievedSubaccount.Name);
             Assert.True(retrievedSubaccount.Active);
-            Assert.True(retrievedSubaccount.AccountId > 0);
+            Assert.NotNull(retrievedSubaccount.workspaceKey);
         }
     }
 }
\ No newline at end of file
diff --git a/SeatsioDotNet.Test/AccountIdAuthenticationTest.cs b/SeatsioDotNet.Test/WorkspaceKeyAuthenticationTest.cs
similarity index 63%
rename from SeatsioDotNet.Test/AccountIdAuthenticationTest.cs
rename to SeatsioDotNet.Test/WorkspaceKeyAuthenticationTest.cs
index 56c234f..02cb08e 100644
--- a/SeatsioDotNet.Test/AccountIdAuthenticationTest.cs
+++ b/SeatsioDotNet.Test/WorkspaceKeyAuthenticationTest.cs
@@ -2,17 +2,17 @@
 
 namespace SeatsioDotNet.Test
 {
-    public class AccountIdAuthenticationTest : SeatsioClientTest
+    public class WorkspaceKeyAuthenticationTest : SeatsioClientTest
     {
         [Fact]
         public void Test()
         {
             var subaccount = Client.Subaccounts.Create();
 
-            var subaccountClient = CreateSeatsioClient(User.SecretKey, subaccount.AccountId);
+            var subaccountClient = CreateSeatsioClient(User.SecretKey, subaccount.workspaceKey);
             var holdToken = subaccountClient.HoldTokens.Create();
 
-            Assert.Equal(subaccount.AccountId, holdToken.AccountId);
+            Assert.Equal(subaccount.workspaceKey, holdToken.workspaceKey);
         }
     }
 }
\ No newline at end of file
diff --git a/SeatsioDotNet/HoldTokens/HoldToken.cs b/SeatsioDotNet/HoldTokens/HoldToken.cs
index d2ee45b..dc7e713 100644
--- a/SeatsioDotNet/HoldTokens/HoldToken.cs
+++ b/SeatsioDotNet/HoldTokens/HoldToken.cs
@@ -9,6 +9,6 @@ public class HoldToken
         public string Token { get; set; }
         public DateTimeOffset ExpiresAt { get; set; }
         public int ExpiresInSeconds { get; set; }
-        public long AccountId { get; set; }
+        public string workspaceKey { get; set; }
     }
 }
\ No newline at end of file
diff --git a/SeatsioDotNet/SeatsioClient.cs b/SeatsioDotNet/SeatsioClient.cs
index 15ac1e5..7761c83 100644
--- a/SeatsioDotNet/SeatsioClient.cs
+++ b/SeatsioDotNet/SeatsioClient.cs
@@ -14,9 +14,9 @@ public class SeatsioClient
         public ChartReports.ChartReports ChartReports { get; }
         public UsageReports.UsageReports UsageReports { get; }
 
-        public SeatsioClient(string secretKey, long? accountId, string baseUrl)
+        public SeatsioClient(string secretKey, string workspaceKey, string baseUrl)
         {
-            var restClient = CreateRestClient(secretKey, accountId, baseUrl);
+            var restClient = CreateRestClient(secretKey, workspaceKey, baseUrl);
             Charts = new Charts.Charts(restClient);
             Events = new Events.Events(restClient);
             Accounts = new Accounts.Accounts(restClient);
@@ -27,7 +27,7 @@ public SeatsioClient(string secretKey, long? accountId, string baseUrl)
             UsageReports = new UsageReports.UsageReports(restClient);
         }
 
-        public SeatsioClient(string secretKey, long? accountId) : this(secretKey, accountId, "https://api.seatsio.net")
+        public SeatsioClient(string secretKey, string workspaceKey) : this(secretKey, workspaceKey, "https://api.seatsio.net")
         {
         }
 
@@ -35,13 +35,13 @@ public SeatsioClient(string secretKey) : this(secretKey, null)
         {
         }
 
-        private static RestClient CreateRestClient(string secretKey, long? accountId, string baseUrl)
+        private static RestClient CreateRestClient(string secretKey, string workspaceKey, string baseUrl)
         {
             var client = new RestClient(baseUrl);
             client.Authenticator = new HttpBasicAuthenticator(secretKey, null);
-            if (accountId != null)
+            if (workspaceKey != null)
             {
-                client.AddDefaultHeader("X-Account-ID", accountId.ToString());
+                client.AddDefaultHeader("X-Workspace-Key", workspaceKey.ToString());
             }
 
             return client;
diff --git a/SeatsioDotNet/Subaccounts/Subaccount.cs b/SeatsioDotNet/Subaccounts/Subaccount.cs
index aa5e91d..5173acb 100644
--- a/SeatsioDotNet/Subaccounts/Subaccount.cs
+++ b/SeatsioDotNet/Subaccounts/Subaccount.cs
@@ -3,7 +3,7 @@
     public class Subaccount
     {
         public long Id { get; set; }
-        public long AccountId { get; set; }
+        public string workspaceKey { get; set; }
         public string SecretKey { get; set; }
         public string DesignerKey { get; set; }
         public string PublicKey { get; set; }