UnicodeDecodeError: 'utf-8' codec can't decode byte 0x99 in position 1: invalid start byte

This error occurs when Python tries to decode a byte string that contains characters that are not valid in the UTF-8 encoding. The byte 0x99 is not a valid UTF-8 character.

To fix this error, you can try the following:

1. Check the encoding of the data source: Make sure that the data you are trying to read is in a format that can be decoded by Python. If the data source is not in UTF-8, you may need to specify the correct encoding when opening the file.

2. Handle the error: You can use the errors parameter of the decode() method to handle errors when decoding the byte string. For example, you can use the 'ignore' option to ignore any invalid characters:

data = b'\x99'
decoded = data.decode('utf-8', errors='ignore')

This will decode the byte string, ignoring any invalid characters.

3. Convert the byte string to a valid UTF-8 string: If you know the encoding of the byte string, you can convert it to a valid UTF-8 string using the decode() method and then encode it back to UTF-8:

data = b'\x99'
decoded = data.decode('iso-8859-1') # Assuming the byte string is in ISO-8859-1 encoding
utf8_encoded = decoded.encode('utf-8')

This will convert the byte string to a valid UTF-8 string.