# FX-SCH-A-000059

Source: https://xmlvalid.com/rules/FX-SCH-A-000059

> If both Invoicing period start date (BT-73) and Invoicing period end date (BT-74) are given then the Invoicing period end date (BT-74) shall be later or equal to the Invoicing period start date (BT-73).

- Level: error
- Rule sets: Factur-X BASIC rules 1.09
- Context: `//ram:ApplicableHeaderTradeSettlement/ram:BillingSpecifiedPeriod`
- Test: `(ram:EndDateTime/udt:DateTimeString[@format = '102']) >= (ram:StartDateTime/udt:DateTimeString[@format = '102']) or not (ram:EndDateTime) or not (ram:StartDateTime)`

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