Presto Pay SDK for Python

Accept payments through the Presto Connect payment gateway from any Python application. The SDK signs every request, verifies every response and webhook, and gives you typed requests and results, so you don't have to handle the gateway's signature scheme yourself.

• Python 3.11+, sync and async with the same API: PrestoPay for Django, Flask and Celery, and AsyncPrestoPay for FastAPI and other asyncio apps
• Two dependencies: cryptography and httpx
• Fully typed: results are frozen dataclasses with snake_case fields

Contents

• Install
• Before you start
• How a payment works
• Quick start
• Payment statuses
• Next steps

Install

pip install presto-pay-sdk

The package imports as presto_pay.

Before you start

1. Create your key pair

You sign every request with your own RSA private key, and Presto verifies it with the matching public key. Generate the pair yourself with openssl; the private key never leaves your systems:

openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out merchant-key.pem
openssl req -new -x509 -key merchant-key.pem -days 3650 -subj "/CN=Your Company" -outform DER -out merchant.der

merchant-key.pem is your private key; keep it secret and out of source control. The SDK also reads a .p12 keystore or an encrypted PEM if that's what you have. Send merchant.der (your public key, in the DER format Presto requires) to Presto.

2. Get your details from Presto

Staging and production are separate: each has its own mid, prestoMrn and Presto certificate, and you register your public key for each. Never mix them.

How a payment works

 Your server                      Presto                     Shopper's browser
     |---- 1. init ------------------>|                              |
     |<--- payment_url ---------------|                              |
     |---- 2. redirect to payment_url ------------------------------>|
     |                                |<---- 3. shopper pays --------|
     |                                |---- 4a. redirect to your redirect_url -->|
     |<--- 4b. webhook to your notify_url                            |
     |---- 5. query ----------------->|                              |

1. Your server calls init with your order's reference and amount. Presto returns a payment_url.
2. You redirect the shopper to payment_url.
3. The shopper chooses a payment method and pays on Presto's page.
4. Presto sends the shopper's browser back to your redirect_url and POSTs a signed webhook to your notify_url. These happen independently and can arrive in either order.
5. On both, you call query to get the payment's status from Presto, and update the order.

The identifiers you'll see:

Quick start

These examples use Flask and the sync PrestoPay. With AsyncPrestoPay the code is the same, but you await each payment call. For Django and FastAPI, see Webhooks.

1. Create the client

Create it once at startup and reuse it. Bad keys or a wrong password fail here, not on the first payment.

from pathlib import Path

from presto_pay import PrestoPay

presto = PrestoPay(
    environment="staging",
    merchant_id="YOUR_MID",
    private_key=Path("merchant-key.pem"),
    presto_public_key=Path("presto.der"),
)

To configure the client from environment variables instead, see Configuration.

2. Start a payment

from flask import redirect

from presto_pay import PaymentMethod, TxnType

payment = presto.payments.init(
    presto_mrn="YOUR_PRESTO_MRN",
    txn_type=TxnType.WEB_PAY,
    txn_ref_num=order_id,
    display_desc=f"Order {order_id}",
    amount=10_000,  # minor units: MYR 100.00
    currency_code="MYR",
    notify_url="https://your-app.example/presto/notify",
    redirect_url=f"https://your-app.example/presto/return/{order_id}",
    allowed_payment_methods=[PaymentMethod.CARD],  # Skip this unless you build your own payment selection page
)

# Save payment.payment_ref_num with the order, then send the shopper to Presto.
if payment.payment_url is None:
    raise RuntimeError(f"Presto returned no payment_url for {order_id}")
return redirect(payment.payment_url)

notify_url must be reachable from the internet; on your own machine, use a tunnel such as ngrok.

3. Show the result on your return page

The redirect only tells you the shopper came back, not whether they paid. Ask Presto:

from presto_pay import PaymentStatus

result = presto.payments.query(presto_mrn="YOUR_PRESTO_MRN", txn_ref_num=order_id)

if result.payment_status == PaymentStatus.AUTHORISED:
    ...  # Paid: show the confirmation.
elif result.payment_status == PaymentStatus.PENDING_AUTHORISE:
    ...  # Not finished yet: show "processing" and check again shortly.
else:
    ...  # Not paid (Failed, Cancelled, Expired, ...): let the shopper try again.

4. Handle the webhook

A webhook tells you something happened to a payment (event_code, and success for whether it worked), not the payment's resulting status, so query for that here too. Verify the raw request body, exactly as received.

from flask import request

from presto_pay import NotifyAck, PrestoPaySignatureError


@app.post("/presto/notify")
def presto_notify():
    try:
        event = presto.webhooks.verify(request.get_data())
    except PrestoPaySignatureError:
        return "", 401  # forged, for another mid, or too old
    except Exception as exc:
        return NotifyAck.for_error(exc), 200, {"Content-Type": NotifyAck.CONTENT_TYPE}  # malformed body

    if not orders.is_event_handled(event.event_ref_num):
        try:
            payment = presto.payments.query(presto_mrn=event.presto_mrn, payment_ref_num=event.payment_ref_num)
            orders.update_status(event.txn_ref_num, payment.payment_status, event.event_ref_num)
        except Exception:
            return NotifyAck.RESEND, 200, {"Content-Type": NotifyAck.CONTENT_TYPE}
    return NotifyAck.OK, 200, {"Content-Type": NotifyAck.CONTENT_TYPE}

NotifyAck.OK tells Presto the event is handled. NotifyAck.RESEND asks Presto to deliver it again (after 1, 2, 5 and 10 minutes), which you want when your own processing failed. Presto redelivers an event with the same event_ref_num, so record it once handled and skip it on later deliveries. See Webhooks for the details.

Update the order the same way from your return page and your webhook: whichever arrives first records the status, and the other finds it already done.

Payment statuses

payment_status is one of these strings; compare it with the PaymentStatus constants.

The gateway can add statuses, so handle an unknown value without failing.

Next steps

• Payments and errors: look up, reverse and refund payments; handle errors, timeouts and retries safely.
• Webhooks: raw bodies, replies, redelivery, deduplication, and complete Django, Flask and FastAPI handlers.
• Production: configuration, keys, several merchants, custom HTTP clients, the go-live checklist and troubleshooting.
• Samples: a runnable checkout against Presto staging, on Flask with PrestoPay (flask-store) and on FastAPI with AsyncPrestoPay (fastapi-store).

Contributing

CONTRIBUTING.md covers building, testing, code style and releasing. Report security issues as described in SECURITY.md, not in a public issue. Real merchant or staging credentials never belong in this repository.

License

Apache License 2.0. See LICENSE.