You can invite UnbelievaBoat to your server by going to https://unbelievaboat.com/invite
This happens if you don't have the
Manage Server permission. You must have that permission to invite bots.
Make sure you are inviting the bot from the correct account.
If this happens, the bot likely lacks permissions to see in the channel you're in.
To check this, you can search in the member list in server settings for UnbelievaBoat.
If the bot is not in there, try re-inviting the bot.