tick.mcfunction not recognised

Hi! I don't know a thing about datapacks tbh (i know commads tho) and i'm trying to update a briliant datapack i found to 1.21 (as it is 1.20 only and I would like to run it on a server for my friends). I've read the wiki to update it but it still doesn't work. I think the issue is that the tick.mcfunction is not registered or running. Can someone help?