Yes, you're writing a fantasy story. Yes, that means many of the normal "rules" of reality are suspended. It doesn't mean you can just write whatever you like and expect your readers to swallow it. The existence of dragons they'll probably accept. Moscow being the capital of France they probably won't.
The key to "selling" weird, fantasy stuff to your reader (like dragons and half-elves) is making the world at large believable. This means getting the simple things right. So on that note:
1. Factual Errors
There are things in the wide-world of fiction that are fantasy elements; things like dragons, unicorns, and women who find beards sexy.