Khalti

Khalti ePayment (KPG-2). The server registers the payment and gets a pidx and payment_url; the user is redirected there.

Environment

What this test shop reads. Values are never shown. Your own app can pass the same values to Config however it likes.

Integrate in your Go app

The same five steps work for every provider — only the constructor changes.

1. Install

   terminalCopy

   go get github.com/mukezhz/pay-np

2. Create the provider

   Build it once at startup and keep it as a paynp.Provider. Load secrets from your config, never the browser.

   setup.goCopy

   import (
       paynp "github.com/mukezhz/pay-np"
       "github.com/mukezhz/pay-np/khalti"
   )
   
   p, err := khalti.New(khalti.Config{
       SecretKey:  khalti.SandboxSecretKey,
       WebsiteURL: "https://shop.example",
   })
   if err != nil {
       log.Fatal(err)
   }
   var provider paynp.Provider = p

3. Start a payment

   Generate a unique TxnID per attempt and store it with the amount and co.ProviderRef — Khalti's Lookup needs it . co.Write redirects or renders the auto-submit form.

   pay.goCopy

   func pay(w http.ResponseWriter, r *http.Request) {
       order := loadOrder(r)                   // your amount, never the browser's
       txnID := newTxnID()                     // unique per attempt, e.g. "ord-42-a1"
       ret := "https://shop.example/return/" + txnID
   
       co, err := provider.Initiate(r.Context(), paynp.InitiateRequest{
           TxnID:       txnID,
           Amount:      order.Amount,          // paynp.Paisa: Rs 1,500 = 150000
           Description: order.Title,
           SuccessURL:  ret,
           FailureURL:  ret + "?failed=1",
       })
       if err != nil {
           http.Error(w, "payment unavailable", http.StatusBadGateway)
           return
       }
       saveAttempt(txnID, order.ID, order.Amount, co.ProviderRef)
       co.Write(w, r)
   }

4. Handle the return, then Lookup

   The redirect is only a hint and is unsigned. Fulfil only when Lookup says SUCCESS; it already checks the amount.

   return.goCopy

   func paymentReturn(w http.ResponseWriter, r *http.Request) {
       _ = r.ParseForm()
       cb, _ := provider.ParseCallback(r.Form)     // may fail on cancel; that's fine
       a := loadAttempt(r.PathValue("txn"))        // amount comes from YOUR records
   
       tx, err := provider.Lookup(r.Context(), paynp.LookupRequest{
           TxnID: a.TxnID, Amount: a.Amount, ProviderRef: a.Ref, Callback: cb,
       })
       switch {
       case errors.Is(err, paynp.ErrAmountMismatch):
           flagForReview(a)                        // never fulfil
       case err != nil:
           // provider unreachable: leave pending, the reconciler retries
       case tx.Status == paynp.StatusSuccess:
           fulfilOnce(a.OrderID, tx.ProviderRef)   // idempotent
       case tx.Status.Final():
           markFailed(a, tx.Status)
       }
       http.Redirect(w, r, "/orders/"+a.OrderID, http.StatusSeeOther)
   }

5. Reconcile pending payments

   Users close the tab after paying and Khalti sends no webhook. Re-run Lookup on attempts that are not final.

   reconcile.goCopy

   for range time.Tick(time.Minute) {
       for _, a := range pendingAttempts(olderThan(2 * time.Minute)) {
           tx, err := provider.Lookup(ctx, paynp.LookupRequest{
               TxnID: a.TxnID, Amount: a.Amount, ProviderRef: a.Ref,
           })
           if err == nil && tx.Status == paynp.StatusSuccess {
               fulfilOnce(a.OrderID, tx.ProviderRef)
           } else if err == nil && tx.Status.Final() {
               markFailed(a, tx.Status)
           }
       }
   }

Mobile apps (Android, iOS, Flutter)

Apps go through your backend: create the payment, open the checkout in an in-app browser, and let the provider return to your server, which runs Lookup and redirects to the app.

Open checkout_url in an in-app browser, or pass provider_ref (the pidx) to Khalti’s Android/iOS/Flutter SDK. Confirm with the status API either way.

POST http://localhost:8080/api/payments
{"provider": "khalti", "amount": "100.00", "app_return_url": "paynp://payment-done"}

→ 201 {"txn_id": "np-…", "status": "PENDING", "provider_ref": "…",
       "checkout_url": "http://localhost:8080/pay/np-…"}

1. Open checkout_url in Custom Tabs / ASWebAuthenticationSession.
2. The provider returns to http://localhost:8080/return/khalti/np-…; the server runs Lookup
   and redirects to paynp://payment-done?txn_id=np-…&status=SUCCESS.
3. Confirm before fulfilling: GET http://localhost:8080/api/payments/np-…
   → {"status": "SUCCESS", "final": true}

Notes

• Minimum amount is Rs 10.
• One return URL for every outcome; the redirect is unsigned, so only Lookup can report SUCCESS.
• Lookup needs the pidx saved from Initiate (Checkout.ProviderRef).

Official docs