Hello @Brendenw, and welcome to the Sendbird community!
I have reached out to our engineering team to look into the cause of the 404 status code for https://repo.sendbird.com/public/maven and I will update you here as soon as I have a response!
I also want to make it known that SyncManager will be deprecated soon and I recommend migrating to Local Caching instead. You can find the doc page for Local Caching here: Local Caching | Chat Android SDK | Sendbird Docs
Where are you receiving the 404 error? Is it in your project or a web browser? If you navigate to that URL in your browser or use Postman, it will return a 404 error.