PO payments under 2000$ include an extra handling & processing fee of 80$. Such payments bare bank commissions from both ends and may take quite a while to collect thus including substantial amount of working hours (invoicing, follow up, collection etc..). By paying online with a credit card you may avoid this charge.

To do so, click on your account name (upper middle part of purple top tool bar) > select settings from drop-down > then select billing tab > click change your payment method button and enter your CC details.