Argument Z must be 2D error while running python code for plotting the data

Question

# Import libraries
from mpl_toolkits import mplot3d
import numpy as np
import matplotlib.pyplot as plt

# Creating dataset
x = np.loadtxt('pfl.dat',unpack=True, usecols=[0])
y = np.loadtxt('pfl.dat',unpack=True, usecols=[1])
z = np.loadtxt('pfl.dat',unpack=True, usecols=[2])

# Creating figure
fig = plt.figure(figsize =(14, 9))
ax = plt.axes(projection ='3d')

# Creating color map
my_cmap = plt.get_cmap('hot')

# Creating plot
surf = ax.plot_surface(x, y, z,
                                        rstride = 8,
                                        cstride = 8,
                                        alpha = 0.8,
                                        cmap = my_cmap)
cset = ax.contourf(x, y, z,
                                zdir ='z',
                                offset = np.min(z),
                                cmap = my_cmap)
cset = ax.contourf(x, y, z,
                                zdir ='x',
                                offset =-5,
                                cmap = my_cmap)
cset = ax.contourf(x, y, z,
                                zdir ='y',
                                offset = 5,
                                cmap = my_cmap)
fig.colorbar(surf, ax = ax,
                        shrink = 0.5,
                        aspect = 5)

# Adding labels
ax.set_xlabel('X-axis')
ax.set_xlim(-5, 5)
ax.set_ylabel('Y-axis')
ax.set_ylim(-5, 5)
ax.set_zlabel('Z-axis')
ax.set_zlim(np.min(z), np.max(z))
ax.set_title('3D surface having 2D contour plot projections')

# show plot
plt.show()

I tried to plot the imported data; but each time I get the same error:

raise ValueError("Argument Z must be 2-dimensional.") ValueError: Argument Z must be 2-dimensional

I searched for similar problems on SO; but did not get any solution.