diff --git a/channels/shangwutong/internal/swt/client.go b/channels/shangwutong/internal/swt/client.go
index 543166a5..3228bd58 100644
--- a/channels/shangwutong/internal/swt/client.go
+++ b/channels/shangwutong/internal/swt/client.go
@@ -197,13 +197,18 @@ func (c *Client) sendHTML(ctx context.Context, session Session, sid, content, op
 		}
 		return SendResult{}, &Error{Operation: operation, Code: "network_error", Retryable: true, Err: err}
 	}
-	status := response.Header.Get("r")
+	status := strings.TrimSpace(response.Header.Get("r"))
+	if !strings.EqualFold(status, "ok") {
+		if protocolError := strings.TrimSpace(response.Header.Get("error")); protocolError != "" {
+			status = protocolError
+		}
+	}
 	result := SendResult{Status: status, Body: body}
-	if status == "ok" {
+	if strings.EqualFold(status, "ok") {
 		return result, nil
 	}
-	retryable := status == "server err"
-	return result, &Error{Operation: operation, Code: normalizeCode(status), Retryable: retryable}
+	code := normalizeCode(status)
+	return result, &Error{Operation: operation, Code: code, Retryable: code == "server_err"}
 }
 
 func (c *Client) SetPresence(ctx context.Context, session Session, presence Presence) error {
diff --git a/channels/shangwutong/internal/swt/client_test.go b/channels/shangwutong/internal/swt/client_test.go
index 765c8965..02e8a851 100644
--- a/channels/shangwutong/internal/swt/client_test.go
+++ b/channels/shangwutong/internal/swt/client_test.go
@@ -68,6 +68,40 @@ func TestClientSendTextEscapesHTML(t *testing.T) {
 	}
 }
 
+func TestClientSendTextClassifiesProtocolStatus(t *testing.T) {
+	tests := []struct {
+		name, status, protocolError, wantCode string
+		wantRetryable                         bool
+	}{
+		{name: "success", status: "ok"},
+		{name: "explicit failure", status: "failed", wantCode: "failed"},
+		{name: "error header", protocolError: "state err", wantCode: "state_err"},
+		{name: "retryable error", protocolError: "server err", wantCode: "server_err", wantRetryable: true},
+		{name: "missing status", wantCode: "missing_status"},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			server := httptest.NewServer(http.HandlerFunc(func(response http.ResponseWriter, _ *http.Request) {
+				response.Header().Set("r", test.status)
+				response.Header().Set("error", test.protocolError)
+			}))
+			defer server.Close()
+
+			result, err := NewClient(rewriteTransportClient(server.URL)).SendText(context.Background(), testSession(), "sid", "hello")
+			if test.wantCode == "" {
+				if err != nil || result.Status != "ok" {
+					t.Fatalf("result = %#v, error = %v", result, err)
+				}
+				return
+			}
+			var protocolErr *Error
+			if !errors.As(err, &protocolErr) || protocolErr.Code != test.wantCode || protocolErr.Retryable != test.wantRetryable {
+				t.Fatalf("result = %#v, error = %#v", result, err)
+			}
+		})
+	}
+}
+
 func TestClientSendFailureBeforeRequestWriteIsRetryable(t *testing.T) {
 	client := NewClient(&http.Client{Transport: roundTripFunc(func(*http.Request) (*http.Response, error) {
 		return nil, errors.New("connection lost")