org.bouncycastle.util.encoders.DecoderException: exception decoding Hex string: invalid characters encountered in Hex string

This exception is thrown when trying to decode a hexadecimal string that contains invalid characters. Hexadecimal strings should only contain characters from 0-9 and A-F (or a-f). If the string contains any other characters, such as spaces or special characters, the decoding process fails and this exception is thrown.

To fix this issue, check the hexadecimal string and make sure it only contains valid characters. If necessary, remove any invalid characters before attempting to decode the string.