/spawnpoint works when used with no arguments. However, adding coordinates (/spawnpoint 0 200 0) results in the error "That player cannot be found". Adding a player name, like my own, "Avantir_Yihn" before the command like the help command instructs (/spawnpoint Avantir_Yihn 0 200 0) results in the error "'Avantir_Yihn' is not a valid number". Adding the name after the coordinates (/spawnpoint 0 200 0 Avantir_Yihn) results in the error "That player cannot be found". This all holds true when using selectors like @a.