Hello David,
Thank you for reaching out to Microsoft Q&A and informed us about the issue. From your report, I believed that it might not be possible to purchase Microsoft Complete on a used Xbox console unless the console was bought new within the last 45 days and you must have the proof of purchase from an authorized retailer. But you can still check the warranty status by:
- Login Microsoft device manager and register your Xbox serial number, from there you can check whether if any warranty or service options are still active or not
You can also contact Microsoft Support to check your console eligibility.
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