Hello , Thanks for your nice paypal payment gateway integration process.all things are ok for me.but i have problem when i want to set currency dynamically . can you help?

$item_1->setName('Item 1') /** item name /
->setCurrency('USD')
->setQuantity(1)
->setPrice($request->get('amount')); / unit price **/
$item_list = new ItemList();
$item_list->setItems(array($item_1));
$amount = new Amount();
$amount->setCurrency('USD')
->setTotal($request->get('amount'));

from the upper code i tried to change setCurrency('USD')
i tried to put a currency code dynamically instead 'USD' simply passing a variable along with paypal checkout form following the code: https://developer.paypal.com/docs/api/reference/currency-codes/ .

but shows this error:
Got Http response code 400 when accessing https://api.sandbox.paypal.com/v1/payments/payment

thanks in advance.