Money marked as received but not in balance?

Hi! I do business through PayPal occasionally when it comes to selling items secondhand, and I just had someone send me 13 Euros to pay off the import fees of their package I shipped to them (I am in the US, they are in the Netherlands). The money is marked as received on my account but it’s not in my balance, so I can’t transfer it out of PayPal. How do I fix this? I’ve never had this happen before. Could it be because PayPal is converting it from euros to USD?