diff --git a/backend/mpc-system/services/session-coordinator/application/use_cases/report_completion.go b/backend/mpc-system/services/session-coordinator/application/use_cases/report_completion.go
index abcb87e8..193ae5b3 100644
--- a/backend/mpc-system/services/session-coordinator/application/use_cases/report_completion.go
+++ b/backend/mpc-system/services/session-coordinator/application/use_cases/report_completion.go
@@ -2,6 +2,7 @@ package use_cases
 
 import (
 	"context"
+	"fmt"
 	"time"
 
 	"github.com/rwadurian/mpc-system/pkg/logger"
@@ -60,15 +61,37 @@ func (uc *ReportCompletionUseCase) Execute(
 	}
 
 	// 3.1 Ensure participant is in Ready state before marking as Completed
-	// The status flow is: Joined -> Ready -> Completed
-	if participant.Status == value_objects.ParticipantStatusJoined {
-		// Auto-transition to Ready if currently Joined
+	// The status flow is: Invited -> Joined -> Ready -> Completed
+	// Handle all possible states to reach Ready
+	switch participant.Status {
+	case value_objects.ParticipantStatusInvited:
+		// Invited -> Joined
+		if err := session.UpdateParticipantStatus(partyID, value_objects.ParticipantStatusJoined); err != nil {
+			return nil, err
+		}
+		logger.Debug("auto-transitioned participant from invited to joined",
+			zap.String("session_id", session.ID.String()),
+			zap.String("party_id", inputData.PartyID))
+		// Joined -> Ready
 		if err := session.UpdateParticipantStatus(partyID, value_objects.ParticipantStatusReady); err != nil {
 			return nil, err
 		}
-		logger.Debug("auto-transitioned participant to ready",
+		logger.Debug("auto-transitioned participant from joined to ready",
 			zap.String("session_id", session.ID.String()),
 			zap.String("party_id", inputData.PartyID))
+	case value_objects.ParticipantStatusJoined:
+		// Joined -> Ready
+		if err := session.UpdateParticipantStatus(partyID, value_objects.ParticipantStatusReady); err != nil {
+			return nil, err
+		}
+		logger.Debug("auto-transitioned participant from joined to ready",
+			zap.String("session_id", session.ID.String()),
+			zap.String("party_id", inputData.PartyID))
+	case value_objects.ParticipantStatusReady:
+		// Already ready, no transition needed
+	default:
+		// Invalid state for completion (Failed, Completed, etc.)
+		return nil, fmt.Errorf("participant in invalid state for completion: %s", participant.Status)
 	}
 
 	// 3.2 Update participant status to completed