Hello Violet,
so how are these Payment Terms ZX11&ZX12 actually customized? Please see SPRO: Materials Management -> Purchasing -> Vendor Master -> Define Terms of Payment. I would guess that even if there is description like "Due 30 days" for ZX12, the actual number of days (ZTAG1) is not maintained.
As for "we don't want to have vuale in EKKO-ZBD1T" -- well, once you have it in customizing for Payment Terms (T052-ZTAG1/ZTAG2/ZTAG3), then it will be copied into PO (EKKO-ZBD1T/ZBD2T/ZBD3T), that's the whole point of having Payment Terms predefined here. If you don't want to have any Payment Terms for given Vendor, that Vendor Master should be maintained accordingly.
Kind Regards
TomT