EResult is the type that is retuned and you can find its full defintiion here
https://partner.steamgames.com/doc/api/steam_api#EResult
The message simply means the API is buisy and didn't take an action ... or so Valve says :)
If you poke around you will see this croups up now and then around UGC/Workshop for people and for different reasons usually related to image upload but occasionaly on create as well, so I would take the route of double checking I have everything set up correctly then asking on the Steamworks SDK dev forums.
If you dont get a good answer there you can submit a ticket to Valve its not all that uncommon for there to be issues with an apps configuraiton either you forgetting to do something or an issue on Valve's side a quick ticket to Valve usually sorts that out. If you do submit a ticket to them detail your issue clearly as well as the troublshooting steps you have already taken.
If you simply say CreatItem is returning an unecpected result they are very likey to point you at the documentation and leave it at that.
As to things to double check
1) The first thing to check is that you have your app ID set up correctly, etc. which I assume you likely do if you have been making other calls and getting the expected results
2) Make sure your project is set up correctly e.g. enable ISteamUGC, etc. and publish the change for it to be commited ... there should be a little checklist thing in your portal page that shows you what all needs to be done.
3) After you have checked all the boxes and your shure this should be working your next step is to ask the community. The Unity community isn't the best option for that, Valve's Steamworks Developer forums will get you better results.
https://steamcommunity.com/groups/steamworks/discussions
Finally we (Heathen Engineering) build an asset that helps make Steamworks integration much simpler and less error prone. As part of that we run a community of 700 or so developer's all Unity devs nearly all using Steamworks so you might find more help there
https://discord.gg/6X3xrRc
While we can only offer proper support for our own code we are happy to chat and offer our experance with the SDK and would be happy to see you in our community.
The message simply means the API is buisy and didn't take an action ... or so Valve says :)
If you poke around you will see this croups up now and then around UGC/Workshop for people and for different reasons usually related to image upload but occasionaly on create as well, so I would take the route of double checking I have everything set up correctly then asking on the Steamworks SDK dev forums.
If you dont get a good answer there you can submit a ticket to Valve its not all that uncommon for there to be issues with an apps configuraiton either you forgetting to do something or an issue on Valve's side a quick ticket to Valve usually sorts that out. If you do submit a ticket to them detail your issue clearly as well as the troublshooting steps you have already taken.
If you simply say CreatItem is returning an unecpected result they are very likey to point you at the documentation and leave it at that.
As to things to double check
1) The first thing to check is that you have your app ID set up correctly, etc. which I assume you likely do if you have been making other calls and getting the expected results
2) Make sure your project is set up correctly e.g. enable ISteamUGC, etc. and publish the change for it to be commited ... there should be a little checklist thing in your portal page that shows you what all needs to be done.
3) After you have checked all the boxes and your shure this should be working your next step is to ask the community. The Unity community isn't the best option for that, Valve's Steamworks Developer forums will get you better results.
https://steamcommunity.com/groups/steamworks/discussions
Finally we (Heathen Engineering) build an asset that helps make Steamworks integration much simpler and less error prone. As part of that we run a community of 700 or so developer's all Unity devs nearly all using Steamworks so you might find more help there
https://discord.gg/6X3xrRc
While we can only offer proper support for our own code we are happy to chat and offer our experance with the SDK and would be happy to see you in our community.