this is something like a bug report, in hopes that the right people will see that. There is an issue with the treasury endpoint for guild leaders.
I made a website that shows all materials needed for a specific guild for the next guild hall upgrade. When I was debugging some visuals, I noticed that others had other amounts of items than I do. I pinpointed it to be based on the language setting
?lang=. At least for french and german, the api shows upgrades that cannot be obtained yet. Our guild is currently lvl 8, so it may be because we do not have unlocked all buildings yet.