A requerimiento is a formal notice from the AEAT (Spanish Tax Agency) that obliges you to do something specific: provide invoices or supporting documents, clarify a figure in a return, or file a missing form. It is never to be ignored: the response period runs from the notification, and not answering turns a routine check into penalties and a bigger case.
Always reply within the period stated in the letter itself, even if only to request an extension when you cannot gather all the paperwork in time. The reply is filed at the sede electrónica, attaching the documents under the requerimiento's reference number.
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