Tag not monitored by Microsoft.
This registration issue must be handled directly by certification support and/or Pearson VUE; it cannot be fixed from the exam scheduling UI.
Since Pearson VUE has already directed the case to Microsoft, the next step is to open a support request with Microsoft Certification Support and provide all the details already listed (name, MS ID, exam code AI-900, error message, and that Pearson VUE referred the case). Certification Support can review the Pearson VUE profile status, any account blocks, and the test-center restrictions on the candidate record, and then coordinate with Pearson VUE if needed.
If the error is related to a Pearson VUE account block (for example, due to payment issues or other profile restrictions), Pearson VUE support must remove that block before registration will work again. In similar registration-block scenarios, the documented guidance is to contact Pearson VUE support via the Microsoft certification channel and/or use the Certification Support path to have the block investigated and lifted.
For general certification and scheduling issues, use the Microsoft Certification Support options referenced in the documentation. If scheduling problems persist after Pearson VUE confirms the account is clear, Certification Support can escalate further.
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