Gain loss for one customer with different currency

Hello all, we can create the transaction with a different currency for one customer if “Allow multi-currency invoices against single party account” checkbox is checked, Now the problem is that I am currently facing this situation

  1. Account currency is set as INR then link that account with one customer

2 . Now there are multiple transactions with different currencies against that customer.

now the problem is how I can make a payment and exchange gain loss against this customer because in the payment entry, the Account Currency is INR. let me know if I am missing something on this Thank you in advance