Field help (FCYTRH) 

This field is used to specify the site to which the purchase orders that you wish to select are attached. The choice of a site thus allows you to filter the selection panel with only the purchase orders recorded on this site. Once the first order has been created, the site is no longer modifiable.
If you wish to save, for a container, orders from different sites (but belonging to the same company), leave that field empty and use the Picking criteria to carry out your selection.