A read is not a write
Reading a customer, an invoice or a payment is how an application stays informed. Proposing a change is the prepared payload: the fields, the identifiers, the checks that already passed. Performing the write is the call that alters the other system.
Not every write needs a person. A low-risk update that the contract allows can run once the checks pass. A write with business impact deserves more care: validation, a precondition that must still be true, approval where the cost of a mistake is high, a repeat that does not create a second record, and a history of what was sent. Doing the step twice must not produce two payments. That is the practical test. Engineers call the property idempotency.
The example on this page holds an accounting write for that reason. The payment event has arrived. The invoice matches. The write has not been sent.