Sometimes it happens because of: rates of the currencies has values with 4 digits after comma and recounting with Paypal for this makes rounding to wrong amount because its operates with 2 digits after comma. To avoid it you are need to set your rates with 2 digits after comma. The main trouble with it - you will have to manually set order to 'Processing' and that is all, no another troubles with it!
You can always set 'Is multiple allowed' to 'No', and your customers will be pay in your basic currency.
There is another radical way: adding some code into woocommerce plugin code
- Open this file: wp-content\plugins\woocommerce\includes\gateways\paypal\includes\class-wc-gateway-paypal-ipn-handler.php
- go to function: private function validate_amount($order, $amount)
- set condition if (!isset($_SESSION['woocs_current_currency'])) as on the screen: