@Alex Oakley Based on the tenant id details provide, I see there are active alerts on your Entra domain services instance AADDS104, AADDS500 & AADDS600.
Please review this documentation to fix alerts - https://learn.microsoft.com/en-us/entra/identity/domain-services/troubleshoot-alerts after which you would be able to change the SKU from standard to enterprise.
Let me know if you have any further questions, feel free to post back.
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