First, search the help docs and this forum. Maybe your question has been answered! The debugging steps can help, too. Still stuck? Delete this line and proceed.
What I’m trying to do
I’m trying to use Obsidian Sync. I have paid for the service. I just get an error message saying, “Your Sync seems to be using Onedrive as a third-party sync service”. I don’t know how to stop Onedrive so I can use Obsidian Sync.
If you want to safely use an Obsidian vault with Obsidian Sync, you need to move that vault outside of the main OneDrive folder. OneDrive also has an option to watch the Documents and Desktop folders, so I would avoid those locations as well (to be safe).