@Allen Brereton - Welcome to Microsoft Q&A and thanks for reaching out to us.
AFAIK the Azure Credits supplied with a Hololens Developer Edition device are not intended to be used to reactivate a deactivated subscription. These credits are intended to be used for development and testing purposes only, and are not transferable or redeemable for cash.
If a user's subscription has been deactivated, they will need to reactivate it using a valid payment method, such as a credit card or PayPal account. Once the subscription has been reactivated, the user can then use any available Azure Credits or other promotional offers to offset the cost of their usage.
Hope this helps. and please feel free to reach out if you have any further questions.
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