LINEAR PHASE FIR DESIGN

I'm designing a low pass linear phase fir filter. To get coefficients i used park mcclellan algorithm. my filter impulse response is not constant 0db in passband but has ripples. I'm adding my own filter code and coefficients and picture of the impulse response.

please tell me where is the proplem.

%%input
x_impulse=zeros(1,256);
   x_impulse(1)=1;
%%coefficients 

function b = coef
%COEF Returns a discrete-time filter object.

% MATLAB Code
% Generated by MATLAB(R) 9.8 and DSP System Toolbox 9.10.
% Generated on: 28-Jul-2020 07:00:26

% Equiripple Lowpass filter designed using the FIRPM function.

% All frequency values are normalized to 1.

Fpass = 0.3;               % Passband Frequency
Fstop = 0.542;             % Stopband Frequency
Dpass = 5.7564627261e-05;  % Passband Ripple
Dstop = 0.001;             % Stopband Attenuation
dens  = 20;                % Density Factor

% Calculate the order from the parameters using FIRPMORD.
[N, Fo, Ao, W] = firpmord([Fpass, Fstop], [1 0], [Dpass, Dstop]);

% Calculate the coefficients using the FIRPM function.
b  = firpm(N, Fo, Ao, W, {dens});
Hd = dfilt.dffir(b);

% [EOF]


%%filter code

function [y] = LFIR(x,b)
    y=zeros(size(x));
    z=zeros(1,2);
    e=0.001;
    for n = 1 : length(x)
        acc=0;
        for k = 1 : length(b)
            if 1+ n-k>0
                z(1,1)=x(1+n-k);
            end
            if 1+n-length(x)+k>0
                z(1,2)=x(1+n-length(x)+k);
            end
            acc=acc+b(1,k)*((z(1,1)+z(1,2)));
            z(1,1)=0+e;
            z(1,2)=0+e;
        end
        y(n)=acc;
    end
end