When you want to create Offline Areas in Field Maps Designer and get the Failed message, it would be really handy to get some detail in a viewable error list to help diagnose any issues.
Further to this, to pre-emp any errors, please add a Sanity Check tool in the Designer so we can do a 'dry run' to check if any of the settings in a map or form may confuse AGOL during the creation of a full fat offline pack.
The dry run would check everything except the geometry, and highlight the typical oversights such as duplicate layers, missing item.json files (no idea why they keep getting lost unless it has to do with the June 2025 Update bugs features).