I have been using ChatGPT for a long time now but only recently set up an API a few days ago. At that time I was able to claim my $18 credit. I told a friend about this and they did the same and got their $18. Then that friend tried to use a second account they had made (different email, same phone number) to build an application, and that second account did not have any credits available. I assume he wasn’t able to claim free credits on that account as OpenAI assigns them based on phone number, not email. Is it possible you’re facing a similar case?
Hope it works out for you, good luck!