Paypal supports a limited number of currencies that causes problems when your customer pays their invoice in a currency that does not supoprted by Paypal. Here is the list of currencies that supported by Paypal: https://developer.paypal.com/docs/api/reference/currency-codes/
What this module does When customer carries out payment in a currency that is not supported by PayPal, this module will convert the payment amount into an amount in a currency (which is configurable) that is supported by Paypal before sending the payment data to Paypal. During payment processing and payment notification, this module ensures that the converted amount is equavalent to the orginal one for full reconciliation. During reconciliation, the difference due to exchange rate will be encoded into the exchange rate journal