ChatGPT Free Plus Trial Fails as System Rejects Every Card Tried

Today, I tried to use the 1-month free Plus membership offer presented to me through the ChatGPT website and mobile app, but the system wouldn't accept any of the cards I tried. Even though I tried different cards, I got a "Your card was declined" message every single time.
There's no sign of any charge or charge attempt on any of the cards, so it doesn't look like a bank-related issue either. Despite this, the system won't activate the membership. I don't understand why I'd be offered a free 1-month Plus membership if the cards aren't going to be accepted anyway, and this situation makes me feel wronged and frustrated.
I haven't reached out to any support channel yet. I'm requesting that my 1-month Plus membership be applied to my account as promised, without any charge being taken from me, and that this issue with the payment system be looked into and fixed.