IIR filter coefficients calculation

I'm trying to design a 'butterworth', 'bandpass' IIR filter using MATLAB. I used designfilt function to design the filter. So using fvtool I can check the info and it shows the filter type is IIR filter But when I used filter function to check the output and used fvtool, in the information it shows that the filter is FIR type. And it shows different numerator and denaminator. Could any one plz tell me what's happening here? Thanks in advance!

d1 = designfilt('bandpassiir','FilterOrder',4, ...
                 'HalfPowerFrequency1',0.5,'HalfPowerFrequency2',6, ...
                 'DesignMethod','butter','SampleRate',Fs);
fvtool(d1)
d = filter(d1,input_signal);
fvtool(d)

Answer 1

[Dhamdhawach Horsuwan]

This is wrong variable type.

d1 is digitalFilter which can visualize with fvtool;

but for d that return from filter is output data or filtered signal.

fvtool only use with filter such as digitalFilter object , filter coefficient[a,b] or sos matrix.