Does the webhook of our payment service make it stateful?

Webhooks by themselves do not make a payment service stateful. Stateful means that the service maintains state between requests, such as sessions or transactional data in memory or a database.

A webhook is a callback mechanism that allows an external service to notify our service about events (for example, a successful payment). Our service can be stateless, simply processing incoming webhooks and updating the state in a database.

If a payment service stores state internally (for example, in memory) and depends on the sequence of webhook calls for correct operation, then it can be considered to have stateful behavior. But usually, the architecture is designed so that the service is stateless, and the state is stored in a database or another storage.

Therefore, the presence of a webhook does not determine whether a service is stateful — it depends on how the storage and management of state are implemented within the service.