You got lucky. Most sites won't let prepaid gift cards go through. For example, neither Amazon nor PayPal, IIRC. Vanilla Visa was exactly the one I had, that ran into the problem, and I'd even put in my name and ZIP on their web site.

The problem seemed to be the lack of a billing address -- what are you supposed to put? Nothing worked. On another site that processed their credit cards via PayPal, it didn't work either. I called PayPal customer service and they explicitly told me they don't support cards that don't provide a means to verify a valid billing address and 3-digit security code.