This I believe is the page that previously said that free trial credits were generated when you have made your first API key and then complete the phone verification invoked at key creation.
https://help.openai.com/en/articles/6613520-phone-verification-faq
It was updated this week, and has no mention of free trial credits.
There is no “help” system document return now for “free” or “trial” search that has any indications of getting a free trial.
The same has been reported by others starting three days ago:
It may be that that the onboarding trial credit program has been quietly discontinued.