diff --git a/connectors/microsoft-teams/element-templates/hybrid/microsoft-teams-outbound-connector-hybrid.json b/connectors/microsoft-teams/element-templates/hybrid/microsoft-teams-outbound-connector-hybrid.json
index a24cd4c9bf..507fec2ebc 100644
--- a/connectors/microsoft-teams/element-templates/hybrid/microsoft-teams-outbound-connector-hybrid.json
+++ b/connectors/microsoft-teams/element-templates/hybrid/microsoft-teams-outbound-connector-hybrid.json
@@ -226,11 +226,8 @@
   }, {
     "id" : "authentication.refresh.clientSecret",
     "label" : "Client secret",
-    "description" : "The secret value of the Azure AD application",
-    "optional" : false,
-    "constraints" : {
-      "notEmpty" : true
-    },
+    "description" : "The secret value of the Azure AD application; optional, depends on whether the client is public or private",
+    "optional" : true,
     "feel" : "optional",
     "group" : "authentication",
     "binding" : {
@@ -386,6 +383,10 @@
     },
     "condition" : {
       "allMatch" : [ {
+        "property" : "data.createChat.chatType",
+        "equals" : "group",
+        "type" : "simple"
+      }, {
         "property" : "data.chatMethod",
         "equals" : "createChat",
         "type" : "simple"
diff --git a/connectors/microsoft-teams/element-templates/microsoft-teams-outbound-connector.json b/connectors/microsoft-teams/element-templates/microsoft-teams-outbound-connector.json
index da99204c46..e60a902743 100644
--- a/connectors/microsoft-teams/element-templates/microsoft-teams-outbound-connector.json
+++ b/connectors/microsoft-teams/element-templates/microsoft-teams-outbound-connector.json
@@ -221,11 +221,8 @@
   }, {
     "id" : "authentication.refresh.clientSecret",
     "label" : "Client secret",
-    "description" : "The secret value of the Azure AD application",
-    "optional" : false,
-    "constraints" : {
-      "notEmpty" : true
-    },
+    "description" : "The secret value of the Azure AD application; optional, depends on whether the client is public or private",
+    "optional" : true,
     "feel" : "optional",
     "group" : "authentication",
     "binding" : {
@@ -381,6 +378,10 @@
     },
     "condition" : {
       "allMatch" : [ {
+        "property" : "data.createChat.chatType",
+        "equals" : "group",
+        "type" : "simple"
+      }, {
         "property" : "data.chatMethod",
         "equals" : "createChat",
         "type" : "simple"
diff --git a/connectors/microsoft-teams/src/main/java/io/camunda/connector/model/Member.java b/connectors/microsoft-teams/src/main/java/io/camunda/connector/model/Member.java
index 58b0247973..04f2fbadae 100644
--- a/connectors/microsoft-teams/src/main/java/io/camunda/connector/model/Member.java
+++ b/connectors/microsoft-teams/src/main/java/io/camunda/connector/model/Member.java
@@ -6,6 +6,7 @@
  */
 package io.camunda.connector.model;
 
+import com.fasterxml.jackson.annotation.JsonAlias;
 import jakarta.validation.constraints.AssertTrue;
 import jakarta.validation.constraints.NotNull;
 import java.util.List;
@@ -15,11 +16,13 @@
 public class Member {
 
   public static final String USER_DATA_BIND = "user@odata.bind";
-  public static final String USER_DATA_TYPE = "@odata.type";
   public static final List<String> OWNER_ROLES = List.of("owner");
 
   private String userId;
+
+  @JsonAlias(value = {"userPrincipalName", "principalName"})
   private String userPrincipalName;
+
   @NotNull private List<String> roles;
 
   @AssertTrue(message = "Missing one of properties : [userId, userPrincipalName]")
diff --git a/connectors/microsoft-teams/src/main/java/io/camunda/connector/model/authentication/RefreshTokenAuthentication.java b/connectors/microsoft-teams/src/main/java/io/camunda/connector/model/authentication/RefreshTokenAuthentication.java
index 2d3108e164..40a4d18d4a 100644
--- a/connectors/microsoft-teams/src/main/java/io/camunda/connector/model/authentication/RefreshTokenAuthentication.java
+++ b/connectors/microsoft-teams/src/main/java/io/camunda/connector/model/authentication/RefreshTokenAuthentication.java
@@ -29,12 +29,13 @@ public record RefreshTokenAuthentication(
             label = "Tenant ID",
             description = "The tenant ID of the application")
         String tenantId,
-    @NotBlank
-        @TemplateProperty(
+    @TemplateProperty(
             group = "authentication",
             id = "refresh.clientSecret",
             label = "Client secret",
-            description = "The secret value of the Azure AD application")
+            optional = true,
+            description =
+                "The secret value of the Azure AD application; optional, depends on whether the client is public or private")
         String clientSecret)
     implements MSTeamsAuthentication {
 
diff --git a/connectors/microsoft-teams/src/main/java/io/camunda/connector/model/request/data/CreateChat.java b/connectors/microsoft-teams/src/main/java/io/camunda/connector/model/request/data/CreateChat.java
index e02d765b2c..25babfdecc 100644
--- a/connectors/microsoft-teams/src/main/java/io/camunda/connector/model/request/data/CreateChat.java
+++ b/connectors/microsoft-teams/src/main/java/io/camunda/connector/model/request/data/CreateChat.java
@@ -36,6 +36,10 @@ public record CreateChat(
             id = "createChat.topic",
             label = "Topic",
             optional = true,
+            condition =
+                @TemplateProperty.PropertyCondition(
+                    property = "data.createChat.chatType",
+                    equals = "group"),
             description = "Set topic of chat (optional)")
         String topic,
     @NotNull
diff --git a/connectors/microsoft-teams/src/main/java/io/camunda/connector/suppliers/GraphServiceClientSupplier.java b/connectors/microsoft-teams/src/main/java/io/camunda/connector/suppliers/GraphServiceClientSupplier.java
index 5b8a6813f6..c3163cbfee 100644
--- a/connectors/microsoft-teams/src/main/java/io/camunda/connector/suppliers/GraphServiceClientSupplier.java
+++ b/connectors/microsoft-teams/src/main/java/io/camunda/connector/suppliers/GraphServiceClientSupplier.java
@@ -22,8 +22,8 @@
 import okhttp3.FormBody;
 import okhttp3.OkHttpClient;
 import okhttp3.Request;
-import okhttp3.RequestBody;
 import okhttp3.Response;
+import org.apache.commons.lang3.StringUtils;
 import org.jetbrains.annotations.NotNull;
 import reactor.core.publisher.Mono;
 
@@ -79,29 +79,31 @@ public GraphServiceClient buildAndGetGraphServiceClient(final String token) {
 
   @NotNull
   private Request buildRequest(final RefreshTokenAuthentication authentication) {
-    RequestBody formBody =
+
+    FormBody.Builder formBodyBuilder =
         new FormBody.Builder()
             .add(CLIENT_ID, authentication.clientId())
             .add(GRANT_TYPE, REFRESH_TOKEN)
-            .add(CLIENT_SECRET, authentication.clientSecret())
-            .add(REFRESH_TOKEN, authentication.token())
-            .build();
+            .add(REFRESH_TOKEN, authentication.token());
+    if (StringUtils.isNoneBlank(authentication.clientSecret())) {
+      formBodyBuilder.add(CLIENT_SECRET, authentication.clientSecret());
+    }
     return new Request.Builder()
         .url(String.format(URL, authentication.tenantId()))
         .header(CONTENT_TYPE, X_WWW_FORM_URLENCODED)
-        .post(formBody)
+        .post(formBodyBuilder.build())
         .build();
   }
 
   private String getAccessToken(final Request request) {
-    try (Response execute = okHttpClient.newCall(request).execute()) {
-      if (execute.isSuccessful()) {
+    try (Response response = okHttpClient.newCall(request).execute()) {
+      if (response.isSuccessful()) {
         return ObjectMapperSupplier.objectMapper()
-            .readTree(execute.body().string())
+            .readTree(response.body().string())
             .get(ACCESS_TOKEN)
             .asText();
       } else {
-        throw new RuntimeException(execute.message());
+        throw new RuntimeException(response.message());
       }
     } catch (JsonProcessingException e) {
       throw new RuntimeException("Error while parse refresh token response", e);