Posting previews, incomplete versions or every campaign map on its own in this section is usually frowned upon.
Map section, in general, is meant for projects that have at least reached a certain degree of completion, not ones that have barely made it off the ground. And a campaign that only has an intro cutscene map definetely qualifies as a project that it's still in its infant stages, not something that's nearing completion.
If you're wondering why things are the way they are - it's for the users. Map section is meant to be a place that you visit to find a relatively complete experience - a map or a campaign that you download and can play through the whole thing, not just get a tiny tease of what it might eventually become.
For that reason, do not be surprised if your map gets rejected or classified as substandard.
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If you want to get feedback on the in-development version of your campaign, a much better place to do this would be here:
Map Development
Create your own thread, tell us something about your campaign - like what story do you want to tell, what are the gameplay features you're going for, etc. Then upload the map directly to Hive either by attaching it to the thread or using the pastebin (just don't forget to post the link to the paste in your thread):
https://www.hiveworkshop.com/pastebin/create
Once that's done, you will have your own thread where you can get feedback on your work, provide development updates and discuss anything about your project