"""Clean and validate the PO Token by stripping invalid characters.

This function processes the input PO Token by decoding it from URL-safe base64, 
then re-encoding it to ensure it is properly formatted. Invalid characters, such as 
additional URL parameters, are removed during this process. If the token is invalid 
or cannot be decoded, a `ValueError` is raised.

Args:
    po_token (str): The PO Token to be cleaned and validated.

Returns:
    str: The cleaned and validated PO Token in URL-safe base64 format.

Raises:
    ValueError: If the PO Token is invalid or cannot be decoded.
"""