Field help (PIHPTE) 

The payment conditions describe the calculation rules of the open item dates in journal entry (orders, invoices and credit memos). The calculated open items can be multiple and with multiple payment modes.
The payment conditions define:

The date used as the calculation starting point can vary with the context (invoice date or receipt date) and it is modifiable in entry mode. It remains modifiable on entry.
The default payment conditions are attached to the BP and are modifiable in entry mode. The payment condition is initialized using the payment condition of the invoicing supplier or the payment condition entered on the first document selected.
Only a discount code consistent with the legislation and company group of the document site can be entered.
SEEREFERTTOThe general principles linked to the multi-legislation setup are detailed here.

Specificities linked to inter-companies: for an intercompany invoice generated from a sales invoices, the payment condition is intialized from the one of the sales invoice.