diff --git a/backend/mpc-system/services/account/adapters/input/http/co_managed_handler.go b/backend/mpc-system/services/account/adapters/input/http/co_managed_handler.go
index 40ecac63..ff89c229 100644
--- a/backend/mpc-system/services/account/adapters/input/http/co_managed_handler.go
+++ b/backend/mpc-system/services/account/adapters/input/http/co_managed_handler.go
@@ -608,6 +608,7 @@ func (h *CoManagedHTTPHandler) CreateSignSession(c *gin.Context) {
 		"invite_code":           inviteCode,
 		"join_token":            wildcardToken,    // Backward compatible: wildcard token (may be empty)
 		"join_tokens":           resp.JoinTokens,  // New: all join tokens (map[partyID]token)
+		"threshold_n":           keygenThresholdN, // Original N from keygen (required for TSS)
 		"threshold_t":           req.ThresholdT,
 		"selected_parties":      resp.SelectedParties,
 		"status":                "waiting_for_participants",