Billing from vendor 10/1 & pymnt on 15/1. what exch rate be used to record expense?10 or 15?

Question

Dr> Expenses (exch rate 10/1 or 15/1 ?)
Cr> Bank (exch rate 15/1)
If payment on 10 Feb then on 31/1 :
Dr> Expenses (exch rate 10/1 or 31/1 ?)
Cr> Account Payable (exch rate 31/1)

Answer 1

The exchange rate on the date that goods or services are received should be used, regardless of the invoice date or the date paid.

Any difference in FX rates between date received & paid is a forex gain or loss.