Uploading model through challenge page
Go to the challenge page and search on the right side of the page for "submit your design now" with a button called "upload model" below it.
When you press this, you will get to the standard upload page, but with the correct tags already filled in for you.
When you don't see your model at the entries, that doesn't mean your model does not participate. It's simply a bug or a delay.
Because of the tag, they will find your model!