diff --git a/backend/internal/payment/provider/easypay.go b/backend/internal/payment/provider/easypay.go
index 37bd38b2..e7d8aab9 100644
--- a/backend/internal/payment/provider/easypay.go
+++ b/backend/internal/payment/provider/easypay.go
@@ -25,6 +25,7 @@ const (
 	easypayStatusPaid      = 1
 	easypayHTTPTimeout     = 10 * time.Second
 	maxEasypayResponseSize = 1 << 20 // 1MB
+	maxEasypayErrorSummary = 512
 	tradeStatusSuccess     = "TRADE_SUCCESS"
 	signTypeMD5            = "MD5"
 	paymentModePopup       = "popup"
@@ -42,17 +43,55 @@ type EasyPay struct {
 // config keys: pid, pkey, apiBase, notifyUrl, returnUrl, cid, cidAlipay, cidWxpay
 func NewEasyPay(instanceID string, config map[string]string) (*EasyPay, error) {
 	for _, k := range []string{"pid", "pkey", "apiBase", "notifyUrl", "returnUrl"} {
-		if config[k] == "" {
+		if strings.TrimSpace(config[k]) == "" {
 			return nil, fmt.Errorf("easypay config missing required key: %s", k)
 		}
 	}
+	cfg := make(map[string]string, len(config))
+	for k, v := range config {
+		cfg[k] = v
+	}
+	cfg["apiBase"] = normalizeEasyPayAPIBase(cfg["apiBase"])
 	return &EasyPay{
 		instanceID: instanceID,
-		config:     config,
+		config:     cfg,
 		httpClient: &http.Client{Timeout: easypayHTTPTimeout},
 	}, nil
 }
 
+func normalizeEasyPayAPIBase(apiBase string) string {
+	base := strings.TrimSpace(apiBase)
+	if base == "" {
+		return ""
+	}
+	if parsed, err := url.Parse(base); err == nil && parsed.Scheme != "" && parsed.Host != "" {
+		parsed.RawQuery = ""
+		parsed.Fragment = ""
+		parsed.RawPath = ""
+		parsed.Path = trimEasyPayEndpointPath(parsed.Path)
+		return strings.TrimRight(parsed.String(), "/")
+	}
+	return strings.TrimRight(trimEasyPayEndpointPath(base), "/")
+}
+
+func trimEasyPayEndpointPath(path string) string {
+	path = strings.TrimRight(strings.TrimSpace(path), "/")
+	lower := strings.ToLower(path)
+	for _, endpoint := range []string{"/submit.php", "/mapi.php", "/api.php"} {
+		if strings.HasSuffix(lower, endpoint) {
+			return strings.TrimRight(path[:len(path)-len(endpoint)], "/")
+		}
+	}
+	return path
+}
+
+func (e *EasyPay) apiBase() string {
+	if e == nil {
+		return ""
+	}
+	return normalizeEasyPayAPIBase(e.config["apiBase"])
+}
+
 func (e *EasyPay) Name() string        { return "EasyPay" }
 func (e *EasyPay) ProviderKey() string { return payment.TypeEasyPay }
 func (e *EasyPay) SupportedTypes() []payment.PaymentType {
@@ -104,8 +143,7 @@ func (e *EasyPay) createRedirectPayment(req payment.CreatePaymentRequest) (*paym
 	for k, v := range params {
 		q.Set(k, v)
 	}
-	base := strings.TrimRight(e.config["apiBase"], "/")
-	payURL := base + "/submit.php?" + q.Encode()
+	payURL := e.apiBase() + "/submit.php?" + q.Encode()
 	return &payment.CreatePaymentResponse{PayURL: payURL}, nil
 }
 
@@ -127,7 +165,7 @@ func (e *EasyPay) createAPIPayment(ctx context.Context, req payment.CreatePaymen
 	params["sign"] = easyPaySign(params, e.config["pkey"])
 	params["sign_type"] = signTypeMD5
 
-	body, err := e.post(ctx, strings.TrimRight(e.config["apiBase"], "/")+"/mapi.php", params)
+	body, err := e.post(ctx, e.apiBase()+"/mapi.php", params)
 	if err != nil {
 		return nil, fmt.Errorf("easypay create: %w", err)
 	}
@@ -171,7 +209,7 @@ func (e *EasyPay) QueryOrder(ctx context.Context, tradeNo string) (*payment.Quer
 		"act": "order", "pid": e.config["pid"],
 		"key": e.config["pkey"], "out_trade_no": tradeNo,
 	}
-	body, err := e.post(ctx, e.config["apiBase"]+"/api.php", params)
+	body, err := e.post(ctx, e.apiBase()+"/api.php", params)
 	if err != nil {
 		return nil, fmt.Errorf("easypay query: %w", err)
 	}
@@ -234,25 +272,128 @@ func (e *EasyPay) VerifyNotification(_ context.Context, rawBody string, _ map[st
 }
 
 func (e *EasyPay) Refund(ctx context.Context, req payment.RefundRequest) (*payment.RefundResponse, error) {
-	params := map[string]string{
-		"pid": e.config["pid"], "key": e.config["pkey"],
-		"trade_no": req.TradeNo, "out_trade_no": req.OrderID, "money": req.Amount,
+	attempts := e.refundAttempts(req)
+	if len(attempts) == 0 {
+		return nil, fmt.Errorf("easypay refund missing order identifier")
 	}
-	body, err := e.post(ctx, e.config["apiBase"]+"/api.php?act=refund", params)
-	if err != nil {
-		return nil, fmt.Errorf("easypay refund: %w", err)
+	var firstErr error
+	for i, attempt := range attempts {
+		body, status, err := e.postRaw(ctx, e.apiBase()+"/api.php?act=refund", attempt.params)
+		if err != nil {
+			return nil, fmt.Errorf("easypay refund request: %w", err)
+		}
+		if err := parseEasyPayRefundResponse(status, body); err != nil {
+			if firstErr == nil {
+				firstErr = err
+			}
+			if i+1 < len(attempts) && isEasyPayRefundOrderNotFound(err) {
+				continue
+			}
+			return nil, err
+		}
+		return &payment.RefundResponse{RefundID: attempt.refundID, Status: payment.ProviderStatusSuccess}, nil
 	}
+	return nil, firstErr
+}
+
+type easyPayRefundAttempt struct {
+	params   map[string]string
+	refundID string
+}
+
+func (e *EasyPay) refundAttempts(req payment.RefundRequest) []easyPayRefundAttempt {
+	base := map[string]string{
+		"pid": e.config["pid"], "key": e.config["pkey"], "money": req.Amount,
+	}
+	var attempts []easyPayRefundAttempt
+	if orderID := strings.TrimSpace(req.OrderID); orderID != "" {
+		params := cloneStringMap(base)
+		params["out_trade_no"] = orderID
+		attempts = append(attempts, easyPayRefundAttempt{params: params, refundID: orderID})
+	}
+	if tradeNo := strings.TrimSpace(req.TradeNo); tradeNo != "" {
+		params := cloneStringMap(base)
+		params["trade_no"] = tradeNo
+		attempts = append(attempts, easyPayRefundAttempt{params: params, refundID: tradeNo})
+	}
+	return attempts
+}
+
+func cloneStringMap(in map[string]string) map[string]string {
+	out := make(map[string]string, len(in))
+	for k, v := range in {
+		out[k] = v
+	}
+	return out
+}
+
+func isEasyPayRefundOrderNotFound(err error) bool {
+	if err == nil {
+		return false
+	}
+	msg := err.Error()
+	lower := strings.ToLower(msg)
+	return strings.Contains(msg, "订单编号不存在") ||
+		strings.Contains(msg, "订单不存在") ||
+		strings.Contains(lower, "order not found") ||
+		strings.Contains(lower, "not exist")
+}
+
+func parseEasyPayRefundResponse(status int, body []byte) error {
+	summary := summarizeEasyPayResponse(body)
+	if status < http.StatusOK || status >= http.StatusMultipleChoices {
+		return fmt.Errorf("easypay refund HTTP %d: %s", status, summary)
+	}
+
+	trimmed := strings.TrimSpace(string(body))
+	if trimmed == "" {
+		return fmt.Errorf("easypay refund empty response (HTTP %d): %s", status, summary)
+	}
+
+	lower := strings.ToLower(trimmed)
+	if strings.HasPrefix(lower, "<!doctype html") || strings.HasPrefix(lower, "<html") ||
+		(strings.HasPrefix(lower, "<") && strings.Contains(lower, "html")) {
+		return fmt.Errorf("easypay refund non-JSON response (HTTP %d): %s", status, summary)
+	}
+
 	var resp struct {
-		Code int    `json:"code"`
+		Code any    `json:"code"`
 		Msg  string `json:"msg"`
 	}
 	if err := json.Unmarshal(body, &resp); err != nil {
-		return nil, fmt.Errorf("easypay parse refund: %w", err)
+		return fmt.Errorf("easypay refund non-JSON response (HTTP %d): %s", status, summary)
 	}
-	if resp.Code != easypayCodeSuccess {
-		return nil, fmt.Errorf("easypay refund failed: %s", resp.Msg)
+	if !easyPayResponseCodeIsSuccess(resp.Code) {
+		msg := strings.TrimSpace(resp.Msg)
+		if msg == "" {
+			msg = summary
+		}
+		return fmt.Errorf("easypay refund failed (HTTP %d): %s", status, msg)
 	}
-	return &payment.RefundResponse{RefundID: req.TradeNo, Status: payment.ProviderStatusSuccess}, nil
+	return nil
+}
+
+func easyPayResponseCodeIsSuccess(code any) bool {
+	switch v := code.(type) {
+	case float64:
+		return int(v) == easypayCodeSuccess
+	case string:
+		n, err := strconv.Atoi(strings.TrimSpace(v))
+		return err == nil && n == easypayCodeSuccess
+	default:
+		return false
+	}
+}
+
+func summarizeEasyPayResponse(body []byte) string {
+	summary := strings.Join(strings.Fields(string(body)), " ")
+	if summary == "" {
+		return "<empty>"
+	}
+	if len(summary) > maxEasypayErrorSummary {
+		return summary[:maxEasypayErrorSummary] + "..."
+	}
+	return summary
 }
 
 func (e *EasyPay) resolveCID(paymentType string) string {
@@ -269,21 +410,34 @@ func (e *EasyPay) resolveCID(paymentType string) string {
 }
 
 func (e *EasyPay) post(ctx context.Context, endpoint string, params map[string]string) ([]byte, error) {
+	body, _, err := e.postRaw(ctx, endpoint, params)
+	return body, err
+}
+
+func (e *EasyPay) postRaw(ctx context.Context, endpoint string, params map[string]string) ([]byte, int, error) {
 	form := url.Values{}
 	for k, v := range params {
 		form.Set(k, v)
 	}
 	req, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, strings.NewReader(form.Encode()))
 	if err != nil {
-		return nil, err
+		return nil, 0, err
 	}
 	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
-	resp, err := e.httpClient.Do(req)
+	client := e.httpClient
+	if client == nil {
+		client = &http.Client{Timeout: easypayHTTPTimeout}
+	}
+	resp, err := client.Do(req)
 	if err != nil {
-		return nil, err
+		return nil, 0, err
 	}
 	defer func() { _ = resp.Body.Close() }()
-	return io.ReadAll(io.LimitReader(resp.Body, maxEasypayResponseSize))
+	body, err := io.ReadAll(io.LimitReader(resp.Body, maxEasypayResponseSize))
+	if err != nil {
+		return nil, resp.StatusCode, err
+	}
+	return body, resp.StatusCode, nil
 }
 
 func easyPaySign(params map[string]string, pkey string) string {
diff --git a/backend/internal/payment/provider/easypay_refund_test.go b/backend/internal/payment/provider/easypay_refund_test.go
new file mode 100644
index 00000000..9e0e4942
--- /dev/null
+++ b/backend/internal/payment/provider/easypay_refund_test.go
@@ -0,0 +1,196 @@
+package provider
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strings"
+	"testing"
+
+	"github.com/Wei-Shaw/sub2api/internal/payment"
+)
+
+func TestNormalizeEasyPayAPIBase(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{input: "https://zpayz.cn", want: "https://zpayz.cn"},
+		{input: "https://zpayz.cn/", want: "https://zpayz.cn"},
+		{input: "https://zpayz.cn/mapi.php", want: "https://zpayz.cn"},
+		{input: "https://zpayz.cn/submit.php", want: "https://zpayz.cn"},
+		{input: "https://zpayz.cn/api.php", want: "https://zpayz.cn"},
+		{input: "https://zpayz.cn/api.php?act=refund", want: "https://zpayz.cn"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			t.Parallel()
+			if got := normalizeEasyPayAPIBase(tt.input); got != tt.want {
+				t.Fatalf("normalizeEasyPayAPIBase(%q) = %q, want %q", tt.input, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestEasyPayRefundNormalizesAPIBaseAndSendsOutTradeNoOnly(t *testing.T) {
+	t.Parallel()
+
+	var gotPath string
+	var gotQuery url.Values
+	var gotForm url.Values
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotPath = r.URL.Path
+		gotQuery = r.URL.Query()
+		if err := r.ParseForm(); err != nil {
+			t.Errorf("ParseForm: %v", err)
+		}
+		gotForm = r.PostForm
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"code":1,"msg":"ok"}`))
+	}))
+	defer server.Close()
+
+	provider := newTestEasyPay(t, server.URL+"/mapi.php")
+	resp, err := provider.Refund(context.Background(), payment.RefundRequest{
+		TradeNo: "trade-123",
+		OrderID: "out-456",
+		Amount:  "1.50",
+	})
+	if err != nil {
+		t.Fatalf("Refund returned error: %v", err)
+	}
+	if resp == nil || resp.Status != payment.ProviderStatusSuccess {
+		t.Fatalf("Refund response = %+v, want success", resp)
+	}
+	if gotPath != "/api.php" {
+		t.Fatalf("refund path = %q, want /api.php", gotPath)
+	}
+	if gotQuery.Get("act") != "refund" {
+		t.Fatalf("refund act query = %q, want refund", gotQuery.Get("act"))
+	}
+	for key, want := range map[string]string{
+		"pid":          "pid-1",
+		"key":          "pkey-1",
+		"out_trade_no": "out-456",
+		"money":        "1.50",
+	} {
+		if got := gotForm.Get(key); got != want {
+			t.Fatalf("form[%s] = %q, want %q (form=%v)", key, got, want, gotForm)
+		}
+	}
+	if got := gotForm.Get("trade_no"); got != "" {
+		t.Fatalf("form[trade_no] = %q, want empty (form=%v)", got, gotForm)
+	}
+}
+
+func TestEasyPayRefundRetriesWithTradeNoWhenOutTradeNoNotFound(t *testing.T) {
+	t.Parallel()
+
+	var gotForms []url.Values
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api.php" {
+			t.Errorf("refund path = %q, want /api.php", r.URL.Path)
+		}
+		if r.URL.Query().Get("act") != "refund" {
+			t.Errorf("refund act query = %q, want refund", r.URL.Query().Get("act"))
+		}
+		if err := r.ParseForm(); err != nil {
+			t.Errorf("ParseForm: %v", err)
+		}
+		gotForms = append(gotForms, r.PostForm)
+		w.Header().Set("Content-Type", "application/json")
+		if len(gotForms) == 1 {
+			_, _ = w.Write([]byte(`{"code":0,"msg":"订单编号不存在！"}`))
+			return
+		}
+		_, _ = w.Write([]byte(`{"code":1,"msg":"ok"}`))
+	}))
+	defer server.Close()
+
+	provider := newTestEasyPay(t, server.URL+"/mapi.php")
+	resp, err := provider.Refund(context.Background(), payment.RefundRequest{
+		TradeNo: "trade-123",
+		OrderID: "out-456",
+		Amount:  "1.50",
+	})
+	if err != nil {
+		t.Fatalf("Refund returned error: %v", err)
+	}
+	if resp == nil || resp.Status != payment.ProviderStatusSuccess || resp.RefundID != "trade-123" {
+		t.Fatalf("Refund response = %+v, want success with trade refund id", resp)
+	}
+	if len(gotForms) != 2 {
+		t.Fatalf("refund attempts = %d, want 2", len(gotForms))
+	}
+	if got := gotForms[0].Get("out_trade_no"); got != "out-456" {
+		t.Fatalf("first form[out_trade_no] = %q, want out-456 (form=%v)", got, gotForms[0])
+	}
+	if got := gotForms[0].Get("trade_no"); got != "" {
+		t.Fatalf("first form[trade_no] = %q, want empty (form=%v)", got, gotForms[0])
+	}
+	if got := gotForms[1].Get("trade_no"); got != "trade-123" {
+		t.Fatalf("second form[trade_no] = %q, want trade-123 (form=%v)", got, gotForms[1])
+	}
+	if got := gotForms[1].Get("out_trade_no"); got != "" {
+		t.Fatalf("second form[out_trade_no] = %q, want empty (form=%v)", got, gotForms[1])
+	}
+}
+
+func TestEasyPayRefundResponseErrors(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name       string
+		statusCode int
+		body       string
+		want       string
+	}{
+		{name: "html response", statusCode: http.StatusOK, body: "<html>bad config</html>", want: "non-JSON response (HTTP 200): <html>bad config</html>"},
+		{name: "non json response", statusCode: http.StatusOK, body: "not json", want: "non-JSON response (HTTP 200): not json"},
+		{name: "non 2xx response", statusCode: http.StatusBadGateway, body: "bad gateway", want: "HTTP 502: bad gateway"},
+		{name: "empty response", statusCode: http.StatusOK, body: "", want: "empty response (HTTP 200): <empty>"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+				w.WriteHeader(tt.statusCode)
+				_, _ = w.Write([]byte(tt.body))
+			}))
+			defer server.Close()
+
+			provider := newTestEasyPay(t, server.URL)
+			_, err := provider.Refund(context.Background(), payment.RefundRequest{
+				OrderID: "out-456",
+				Amount:  "1.50",
+			})
+			if err == nil {
+				t.Fatal("Refund returned nil error")
+			}
+			if !strings.Contains(err.Error(), tt.want) {
+				t.Fatalf("Refund error = %q, want substring %q", err.Error(), tt.want)
+			}
+		})
+	}
+}
+
+func newTestEasyPay(t *testing.T, apiBase string) *EasyPay {
+	t.Helper()
+
+	provider, err := NewEasyPay("test-instance", map[string]string{
+		"pid":       "pid-1",
+		"pkey":      "pkey-1",
+		"apiBase":   apiBase,
+		"notifyUrl": "https://example.com/notify",
+		"returnUrl": "https://example.com/return",
+	})
+	if err != nil {
+		t.Fatalf("NewEasyPay: %v", err)
+	}
+	return provider
+}