I used this as an excuse to start a community, just so I could try to reproduce your problem. But, it actually worked for me on the first try, simply by using a single word without any special characters. Similar to your “pens” attempt. FWIW the only other field I filled in was the Display Name, for which I used the same word but starting with a capital letter. For Languages, I selected English.
Anyone else having trouble connecting to slrpnk.net? Both the site and the Lemmy instance (via Jerboa) seem unreachable.
edit: and it’s back online