SpecificationError: nested renamer is not supported

This error typically occurs when using the Pandas `rename()` method and attempting to use a nested dictionary as the `mapper` argument.

For example, consider the following code:

import pandas as pd

data = {'name': ['Alice', 'Bob', 'Charlie'], 'age': [25, 30, 35]}
df = pd.DataFrame(data)

df.rename(columns={'name': {'first_name': 'name', 'last_name': 'surname'}}, inplace=True)

This code will result in the `SpecificationError: nested renamer is not supported` error, because the `rename()` method does not support nested dictionaries for the `mapper` argument.

To fix this error, you can use separate `rename()` calls for each level of renaming, like this:

df.rename(columns={'name': 'first_name'}, inplace=True)
df.rename(columns={'first_name': 'name', 'last_name': 'surname'}, inplace=True)

This will perform the same renaming operation as the original code, but without the nested dictionary.