TypeError: 'norm' must be an instance of matplotlib.colors.Normalize or None, not a type

This error occurs when the variable passed as the `norm` argument to a matplotlib function is not an instance of `matplotlib.colors.Normalize` or `None`.

To fix this error, make sure that the variable you are passing as `norm` is an instance of `matplotlib.colors.Normalize` or `None`. If it is not, you can create an instance of `Normalize` using the `matplotlib.colors.Normalize` class or set `norm=None` to use the default normalization.

For example:

import matplotlib.pyplot as plt
import matplotlib.colors as mcolors

norm = mcolors.Normalize(vmin=0, vmax=1)
plt.scatter(x, y, c=z, cmap='viridis', norm=norm)

Or:

plt.scatter(x, y, c=z, cmap='viridis', norm=None)