What is wrong with my Floyd-Steinberg dithering implementation?

I have implemented the algorithm in python. When I run the code, it returns an image with strange patterns ( black spots ). I've reviewed it multiple times, but I cant find what the problem might be. I have also tried changing the direction in which the algorithm runs, but its no use.

import cv2 as cv
from matplotlib import pyplot as plt 
import numpy as np 

def Dither(img):

    output = np.copy(img)

    for y in range(1,img.shape[0]-1):
        for x in range(1,img.shape[1]-1):
        
            pix = output[y][x]
            newpix = round(pix/255) * 255

            error = pix - newpix

            output[y][x] = newpix

            output[y    ][x + 1] += error * 7/16
            output[y + 1][x - 1] += error * 3/16
            output[y + 1][x    ] += error * 5/16
            output[y + 1][x + 1] += error * 1/16

    return(output)


img = np.array(cv.cvtColor(cv.imread("kitten.jpg"), cv.COLOR_BGR2GRAY))

plt.imshow(Dither(img), cmap="gray")
plt.show()

The reason why the x and y variables are assigned in an unconventional order is that I have googled an implementation which had its variables flipped as well.

My result: my result

Expected result: expected result