I am having a number of people buy gift subscriptions and the credit card ends up not going through. I was testing the process tonight and realized that, for gift subscriptions, Subbly is auto populating the zip code field for credit cards with the SHIPPING zip code, not the billing zip code. This could account for why a number of my subscribers buying gift subscriptions are having issues with payment.
Please see this video that shows what is happening: https://vimeo.com/778719669/10de187f3f