Error: quota exceeded check your plan and billings

Agreed, the only thing I am thinking is that it might be a daily rate limit rather than a spend limit, i.e. you have reached a usage limit for fine-tunes, (example limits below) It could totally be an error in the system not related to that. You should as a matter of course contact help.openai.com and use the bot in the bottom right corner to log your contact details and let them know your issue.