Whilst it is not possible for WHMCS to obtain the rates for PKR, as this is not provided y the data feed from the ECB, using the hook https://developers.whmcs.com/hooks-reference/everything-else/#fetchcurrencyexchangerates, it is possible for you to obtain the exchange rate yourself and apply it to your WHMCS.

We are currently seeking feedback on an alternative currency exchange rate source in this request: https://requests.whmcs.com/idea/change-currency-rate-source