Do I have to pay something after 30 days?
At the end of your first 30 days, you can continue using your free products after you upgrade your account to a pay-as-you-go pricing and remove the spending limit. If you stay within the service quantities included for free, you won’t have to pay anything. The $200 free credit acts as a spending limit.
https://azure.microsoft.com/en-us/free/free-account-faq/
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