Hi Pete,
At the end of the first 30 days of your Azure Free account, you must upgrade it to Pay-As-You-Go to continue using it. If you don't upgrade, your subscription will be automatically disabled.
Excerpt from this Reactivate a disabled Azure subscription article:
Your credit is expired When you sign up for an Azure free account, you get a Free Trial subscription, which provides you $200 Azure credit in your billing currency for 30 days and 12 months of free services. At the end of 30 days, Azure disables your subscription. Your subscription is disabled to protect you from accidentally incurring charges for usage beyond the credit and free services included with your subscription. To continue using Azure services, you must upgrade your subscription. After you upgrade the subscription, you still have access to free services for 12 months. You only get charged for usage beyond the free service quantity limits.
After you upgrade your subscription, you will still have access to certain Azure services that are free for the remainder of the one year since you originally signed up plus other services that are "always free".
Additionally, you will have access to services that are not free, so you have to be careful when creating/using Azure services to stay within the free offer if you want to avoid costs. Please see article below for help avoiding charges.
Avoid charges with your Azure free account
https://learn.microsoft.com/en-us/azure/cost-management-billing/manage/avoid-charges-free-account
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP