If you are still on Twitter and haven't announced your Mastodon handle to your followers, do so now.
#Twitter is blocking #Mastodon domains. For example, while you can still search for and see the word #hachyderm in people's Twitter names and bios on the bird turd, hachyderm.io has been blocked. This means no one on that instance can include their Mastodon domain in a new tweet.
If you haven't fully moved yet, when you finally decide to, you may not be able to tweet your new address.