Depends on where you want to make the purchase from.
On the FITE Website you will have the option to use your Credit Card, Debit Card or Pre-Paid card or use PayPal
In the FITE mobile app your purchase will go through iTunes and Google Play depending on your platform.
In the FITE ROKU Channel your purchase will go through the ROKU purchase interface.
If you are using Amazon Coins or any giftcards you might need to pay extra tax depending on the store you are purchasing from. Contact their respective support if you have trouble purchasing.