IDDQD

No, it needs to be the sale ID.

Ok, now I see that I can get sale ID in IInventory/Deposit results.

Thank you very much for your patience and help.

You can list items in your OPSkins inventory for sale. Look into the ISales/EditPrice API method.

That's great, thanks!

One more question, am I right that saleid in this method may contain assetid of the target item?

You must be sending the wrong ID to OPSkins then.

I've checked assetid, contextid and appid many times and they're correct 

I already have some items in my OPSkins Inventory.

Is it possible to list for sale these items using API?

Or Steam Inventory is the only source?

Marketability isn't the same as tradability.

Yes, I know. Steam says 

tradable: true

 for this item when I request an Inventory with Steam API

UPD: 

Also, I see this item on Opskins "Sell" page, where it says "Your Steam Inventory Displaying tradable items only".

So, it's in my Steam Inventory, it's tradable, I can deposit and sell it manually, but I still cannot list it for sale using Opskins API

That error happens when you're trying to list something that isn't in your Steam inventory (or isn't tradable).

Yes, but it IS in my Steam inventory and tradable (I can sell it on Steam Market). 

Anything else that might help to solve this?

Hello Dr. McKay,

First of all, I'd like to thank you for a great OPSkins API module for Node.js that I'm currently using. 
It makes my work so much easier.

Unfortunately, I have a trouble with its listItems method.
The problem is that method always returns the same error: 

Error: One or more items are no longer in your inventory.

There are two questions that may help me to solve this problem:

1) Where I should have that item I'm trying to sell? In my Opskins Inventory OR in my Steam Inventory? 
I've tried both and the error is still same for each case. Although, when item is in my Opskins inventory, I can list it for sale manually via opskins.com without any problem, but not using opskins.listItems() API method.

2) Are there any other possible reasons for this error to show up?

Thanks in advance.

PS: sorry for my crappy English, I'm still learning it.