STO accepts Visa prepaid cards, but it's much better if you have a Paypal account and tie the card to that account. I tried to pay with my prepaid card just as is [without linking it with Paypal] and it refused it every time.
Create your Paypal account
Log into STO's LTS section
Click "Buy Now"
Click on "Pay with Paypal"
Enter your username and password
Click Pay Now, but make sure that your prepaid credit card is one of the forms of payment being used.
After that, STO will process your payment and, if you have enough on the card, you'll get a confirmation saying "Your lifetime subscription is now active" [or something similar].