ChatGPT Plus Free Trial Fails at Checkout With No Clear Reason

Today, I tried to use the 1-month free Plus offer available through my ChatGPT/OpenAI account, but I ran into a problem at the payment stage. First, I got a warning saying "your card was declined," and then I encountered a message saying "your payment was not approved."
I tried to make the payment with my Ziraat Bank card. I then called my bank, and during that call, I was told there was no issue with my card or my bank, and that the problem didn't appear to be coming from the bank's side. Despite this, I couldn't complete the transaction and wasn't able to take advantage of the 1-month free Plus offer. Right now, my Plus subscription hasn't started at all, and I still can't access the offer.
I am requesting that the promised 1-month free Plus subscription be applied to my account without any additional charge, and that the issue on the payment screen be investigated so I don't run into it again.