Super Mario Maker Bookmark site appears to be having issues locating levels. This is usually a temporary issue. No levels can be added while the site is down. But existing levels should continue to work!
Super Mario Maker 2 - Validation System
Operational
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Warp World is a free application to help you connect your Twitch viewers to you! Use it to easily manage your level queues, allow viewers to directly add levels in chat, and much more!