Field help (PYHFCY) 

Specify the site to which the payment should be made or from which it should be issued. It is initialized by the site associated with the user code. it can be modified provided it is chosen from the list of authorized sites.
If the payment is assigned to an entry batch, the specified site must belong to the company of the entry batch.

When the payment is posted, entry of the cash account will be made on the site specified here.