I'm a frequent user and fan of Privacy.com, however I've had merchants decline charges when I provide a proxy card, only to have the charge succeed when I provi

I'm a frequent user and fan of Privacy.com, however I've had merchants decline charges when I provide a proxy card, only to have the charge succeed when I provide a real card linked to the same account as the aforementioned proxy card. I suspect that Privacy.com uses gift cards as proxies, and some merchants reject payments made with gift cards. If so, this could be why I experienced the above. If someone knows better than I do, please correct me. Genuinely curious how the service works under the hood.