Dutch to English Bus/Financial Business/Commerce (general) Purchase order

I am translating the conditions attached to a Belgian purchase order. It states that the invoice needs to contain a specific wording - but cannot seem to find a standard translation for this (I assume there must be one).

The section reads as follows:

"De facturen dienen opgesteld te worden in 2 exemplaren ... onder vermelding "Voor echt en waarachtig verklaad voor de som van..." en gezonden naar volgend adres:"