[Crayder]

There are better ways, but rearranging your code will do fine:

pawn Код:

if(strlen(params) != 4) return SendClientMessage(playerid, COLOR_WHITE, "SERVER: The pincode must be 4 digits.");
        if(sscanf(params, "d", pass)) return SendClientMessage(playerid, COLOR_WHITE, "USAGE: /changeadminpin [Pin code]");