I keep getting this error:

Oh No! Pet names can only contain letters, numbers, and the following punctuation: periods(.), spaces( ), dashes(-), and underscores (_)

But the name I chose isn't taken (I checked) and it's only one word, no spaces before or after or in between. I've tried a few different names, but the error is exactly the same.

there is a bug report about this: Scootle adopting error . So its not just you and you aren't doing anything wrong. If you post to that thread, you'll get a notice when/if staff post there.