Calum Leslie is a user on mastodon.social. You can follow them or interact with them if you have an account anywhere in the fediverse.
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@zootm other than having to put in the fully qualified @ name? Worked reasonably well when I tried earlier... (still getting used to this thing too, though)
@musicog It was difficult to figure out where to put the ID -- in the end I URL hacked your page URL and used the "remote follow" button
@zootm The easiest way is to use the 'search' box right above the new toot box, and search for their username@instance.