To fix this issue your Tenant needs to be added to a sending exclusion for 60 days to allow them to use blocked IPs whilst they still have a new/trial license. Refer to this documentation for more details.
If your issue is not resolved, Please raise a case with MS Support team from your tenant where you are facing issue, respective team will provide exclusion for your tenant.
You can raise support ticket from aad.portal.azure.com
Hope this helps.
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