If you started your account a while ago, it may have run out. https://azure.microsoft.com/en-us/free/free-account-faq/
This can also happen if you have exceeded the limits of the service and have not been using the free products. https://learn.microsoft.com/en-us/azure/cost-management-billing/manage/mca-check-azure-credits-balance?tabs=portal
I would recommend creating a free ticket with the Billing team if you have further questions.