The company's accounting periods — the months a journal entry may post into (CompanyMember read).

A period belongs to one fiscal year and carries period_no (1..12 within the year), date_from/date_to and a status: open accepts postings, soft_closed still accepts them, and closed/year_closed refuse them — a posting date inside a closed period fails until an accountant explicitly reopens the period (POST …/gl/periods/{period_id}/reopen, reason required, recorded in the close-run ledger — ZET-161). fiscal_year_id narrows to one year; omitted, every year's periods come back.

This is not the VAT filing calendar — those are the gl_vat_period rows of GET …/gl/vat/periods, which have their own quarterly/monthly cadence and their own filed/paid sealing. Use this list to find the period_id a manual journal entry needs, and to check why a posting date was refused.