What does it mean when iconv warns of an invalid character in the input string?

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When iconv warns of an invalid character in the input string, it means that the character encoding in the input string is not recognized, or the input string includes characters that are not valid in the specified encoding. This warning indicates that the conversion may not be accurate, and additional steps may be required to ensure the correctness of the output. The warning can also occur when the input string is corrupted or does not conform to the expected format. To resolve the issue, you may need to check the input string's encoding or use a different encoding or tool for the conversion.