You can't use natives like that. This is correct:
PHP Code:
new name[32]
get_user_name(playerid, name, charsmax(name))
You need to assign a variable and select where to store the name with given maximum characters.
Charsmax gets the maximum lenght that a string array can contain, it's the same as sizeof(name) - 1 (in this case, that's the same as 31).
Then the player name is stored into the "name" string.
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