This error usually indicates a transaction or account issue. Follow these steps:
It's a code like 8015190A or 8007000E. Search it on Xbox Support for specific fixes.
Visit Xbox Live Status for store outages.
The item may be temporarily pulled. Try later or search for the exact title.
Hold power button 10s → unplug 30s → plug in → restart.
Settings → System → Storage → Clear Local Saved Game Cache (keeps cloud saves).
If unresolved, contact Xbox Support with the status code, item name, and steps tried.