Here you set documents with VAT reverse charge (the customer accounts for the tax).
Per the VAT exemption reasons – myDATA table: you send myDATA code 16 (“Without VAT”). In the new VAT Code (Law 5144/2024) this is Article 45; in the old Code (Law 2859/2000) it was Article 39a.
This is not the used-goods margin scheme: there the old law says Article 45, the new law Article 52, and myDATA is code 22 — see used-goods document setup.
Use this when the customer accounts for VAT (e.g. recyclables, emission allowances, mobiles/tablets/laptops, etc.).
Open Settings → Tax connections → Variable mapping and fill the yellow myDATA fields on the related document / VAT. The basics are in myDATA settings.
The myDATA exemption reason is code 16. Do not confuse it with code 22 (used-goods margin).