@EmmaKennedy Hi! I think because Katy is on a different server, you would need to use the full address: either https://mas.to/@katybrand or @katybrand If you are referencing someone on the same server as you, it looks like you can get away with just the first part: @_crp_ for example.
@EmmaKennedy So, when I published that it converted them to clickable links, so it might not obvious what I typed to get them. I used https:// mas.to / @ katybrand or @ katybrand @ mas.to without the spaces. Hope that's helpful.