diff --git a/backend/mpc-system/services/service-party-app/electron/main.ts b/backend/mpc-system/services/service-party-app/electron/main.ts
index 3d484edd..8a0efac2 100644
--- a/backend/mpc-system/services/service-party-app/electron/main.ts
+++ b/backend/mpc-system/services/service-party-app/electron/main.ts
@@ -549,6 +549,8 @@ function setupIpcHandlers() {
   // 加入会话
   ipcMain.handle('grpc:joinSession', async (_event, { sessionId, partyId, joinToken, walletName }) => {
     try {
+      debugLog.info('grpc', `Joining session: sessionId=${sessionId}, partyId=${partyId}, has_token=${!!joinToken}, token_length=${joinToken?.length || 0}`);
+
       const result = await grpcClient?.joinSession(sessionId, partyId, joinToken);
       if (result?.success) {
         // 设置活跃的 keygen 会话信息
@@ -686,7 +688,11 @@ function setupIpcHandlers() {
   // gRPC - 验证邀请码 (通过 Account 服务 HTTP API)
   ipcMain.handle('grpc:validateInviteCode', async (_event, { code }) => {
     try {
+      debugLog.info('account', `Validating invite code: ${code}`);
       const result = await accountClient?.getSessionByInviteCode(code);
+
+      debugLog.info('account', `Got session for invite code: session_id=${result?.session_id}, has_join_token=${!!result?.join_token}, token_length=${result?.join_token?.length || 0}`);
+
       return {
         success: true,
         sessionInfo: {
@@ -703,6 +709,7 @@ function setupIpcHandlers() {
         joinToken: result?.join_token,
       };
     } catch (error) {
+      debugLog.error('account', `Failed to validate invite code: ${(error as Error).message}`);
       return { success: false, error: (error as Error).message };
     }
   });
diff --git a/backend/mpc-system/services/service-party-app/src/types/electron.d.ts b/backend/mpc-system/services/service-party-app/src/types/electron.d.ts
index ba8bf52e..76ee1496 100644
--- a/backend/mpc-system/services/service-party-app/src/types/electron.d.ts
+++ b/backend/mpc-system/services/service-party-app/src/types/electron.d.ts
@@ -132,6 +132,7 @@ interface JoinSessionResult {
 interface ValidateInviteCodeResult {
   success: boolean;
   sessionInfo?: SessionInfo;
+  joinToken?: string;
   error?: string;
 }
 
diff --git a/backend/mpc-system/services/session-coordinator/application/use_cases/join_session.go b/backend/mpc-system/services/session-coordinator/application/use_cases/join_session.go
index f0a3706e..808a520d 100644
--- a/backend/mpc-system/services/session-coordinator/application/use_cases/join_session.go
+++ b/backend/mpc-system/services/session-coordinator/application/use_cases/join_session.go
@@ -59,9 +59,27 @@ func (uc *JoinSessionUseCase) Execute(
 	ctx context.Context,
 	inputData input.JoinSessionInput,
 ) (*input.JoinSessionOutput, error) {
+	// Debug: log token info
+	tokenLen := len(inputData.JoinToken)
+	tokenPreview := ""
+	if tokenLen > 20 {
+		tokenPreview = inputData.JoinToken[:20] + "..."
+	} else if tokenLen > 0 {
+		tokenPreview = inputData.JoinToken
+	}
+	logger.Debug("JoinSession: parsing token",
+		zap.String("session_id", inputData.SessionID.String()),
+		zap.String("party_id", inputData.PartyID),
+		zap.Int("token_length", tokenLen),
+		zap.String("token_preview", tokenPreview))
+
 	// 1. Parse join token to extract session ID (in case not provided)
 	claims, err := uc.tokenValidator.ParseJoinTokenClaims(inputData.JoinToken)
 	if err != nil {
+		logger.Error("JoinSession: failed to parse token",
+			zap.String("session_id", inputData.SessionID.String()),
+			zap.String("party_id", inputData.PartyID),
+			zap.Error(err))
 		return nil, err
 	}