@Ray Greetings!
AFAIK, Azure is not directly available to users in Nigeria. Azure services are offered through trusted partners. This could be a reason for card not accepted while trying to activate Azure Founders credit. Please refer to the FAQ page here - https://learn.microsoft.com/en-us/azure/education-hub/azure-dev-tools-teaching/program-faq
Reference link for Azure in Nigeria - https://www.microsoft.com/mea/trustedcloud/nigeria/
For now, I would suggest reaching out to Microsoft nonprofit support or Azure billing team by raising a support request. The ticket enables you to work closely with the support engineers and get a quick resolution to your issue.
Here is the link - https://docs.microsoft.com/en-us/azure/azure-portal/supportability/how-to-create-azure-support-request to create support case.
FYI: Azure Billing and Subscription Management support is included in the Basic Support Plan without any charge.
https://azure.microsoft.com/en-us/support/plans/
Hope this helps!
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