Collected Art: found no valid post with that title.

Collected Art: found no valid post with that title.

So I'm submitting art to my project. When I add the whole URL to the asset:

Collected Art: found no valid post with that title.

When I add the asset name from the URL to my project:

Collected Art: found no valid post with that title.

When I add the URL to one of the files in that asset:

Collected Art: found no valid post with that title.

With no instructions what to put in the asset list, what do you guys expect will happen?

Google gives no useful information for this problem either.