Spanish term (edited): aviso de siniestro

vs. notificación de ocurrencia de siniestro : (form for) notification of occurrence of loss (incident). Marine or military: casualty, though Lloyds of London insurance translators have never been specific to me about UK - let alone US Am. usage.

Siniestro often coincides in an ins. / reins. co.'s accounts with a claim made.

'First notice of loss starts the wheel of the claims cycle and is when the policyholder notifies the insurer of an unfortunate event.'

It's about a written notice sent to advise of someone's intention to claim for losses resulting from an incident. There's no indication about what the incident was, but that an administrator shall forward the notice to the insurers with the report from the claimant.
Note that
'la plataforma de cálculo'
can be either the computer registration or the calculation.

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Note added at 11 hrs (2022-02-23 23:51:27 GMT)
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ES:
Se trata de una notificación enviada sobre una intención de reclamar como consecuencia de un incidente. No explica lo que era el incidente. Sólo consta que la notificación se pasa a la empresa de los aseguradores con un informe del grupo que reclama.

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Note added at 5 days (2022-02-28 20:42:17 GMT)
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Note that the person who chooses to pursue must first of all claim that an incident took place. The person may also wish to advise that an incident has its importance, which intelligent people know to consider seriously.