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The webhook simulator sends one preset JSON event through a server-side proxy to an address you enter, and reports the status, the latency and the body that came back. That is worth doing. It tells you the endpoint is reachable from outside your own network, that it parses a body it was not expecting, and how a request fares through your load balancer, read against your own logs.

It is worth being equally clear about what it cannot tell you. Nothing is signed, so signature checking goes untested. The request arrives from the proxy, so an address allowlist proves nothing here. One event sent once says nothing about what your handler does with the same event twice.

"There is no API reference here, so there is nothing to evaluate." The first half is accurate. This page publishes no endpoints, no authentication steps and no schema.

The second half is worth arguing with, because a field list is rarely what costs the engineering time. What costs it is the state machine: which states a record can hold, which transitions are legal, which are terminal, and what happens to a record that is accepted and then fails afterwards.

A schema names fields and answers none of that. Ask instead for the list of states and reason codes, and for one worked example of a record that failed after acceptance.

The payload builder gives you a generic amount and a currency code. The shape is right. The thing that breaks an integration sits one level below it.

ISO 4217 assigns every currency a minor-unit exponent: two for most, zero for the Japanese yen, three for the Kuwaiti dinar. Code that multiplies every amount by a hundred sends a tenth of the intended amount to Kuwait and a hundred times too much to Japan. Nothing in either request is malformed. A number in the right field is all either side agreed to check, so nothing on the way in raises an error.

The standard is not the last word either: at least one large processor documents its own table, differing from ISO for a handful of currencies, and tells integrators to follow that instead.