A Haystack component that prepares a payment request instead of paying: agent proposes, human signs

[send21io]

I'm with send21 (disclosure).

The setup: a pipeline that turns a finished job (a quote, a timesheet summary) into something the client can pay. The last component should produce a pay link, never a payment. send21 prepares payment instructions; the payer signs in their own wallet and the money goes straight to your address.

1. The component

from haystack import component

@component
class PayLinkMaker:
    def __init__(self, payee: str):
        self.payee = payee  # your own EURC address on Base

    @component.output_types(pay_link=str, request_id=str)
    def run(self, amount: float, currency: str, order_id: str):
        r = send21_call("create_payment_request", {  # MCP call to send21.io/mcp (helper, not shown)
            "fiatAmount": amount, "fiatCurrency": currency,
            "options": [{"currency": "Eurc", "network": "Base", "address": self.payee}],
            "orderId": order_id, "memo": f"Order {order_id}",
            "expiryHours": None, "idempotencyKey": order_id,
        })
        return {"pay_link": "https://send21.io" + r["payPath"], "request_id": r["id"]}

2. Wiring. Connect a parser's amount/order_id outputs into PayLinkMaker with pipeline.connect(...). The key it uses can create requests but cannot move funds.

3. Closing the loop. The pipeline ends at the link. "Paid" arrives later as a webhook: check X-Send21-Signature (sha256 HMAC of the raw body), then mark the order paid on draft.confirmed. On draft.amount_mismatch (a transfer within 10% of the billed amount), flag it for a person and don't mark it paid.

Not an official Haystack integration.

Question: for an event that arrives hours later, do you start a second pipeline from the webhook, or keep state outside Haystack and only use pipelines for the synchronous part?

Webhook receiver and MCP client examples: https://github.com/send21io/send21-examples

send21, info@send21.io