The error message "Mandatory parameter 'timestamp' was not sent, was empty/null, or malformed" indicates that a required parameter, namely the timestamp parameter, was either not sent at all, sent as empty or null, or was not properly formatted. This can happen when using the Binance REST API in C++ if the code does not properly include the timestamp parameter in the request or if there are formatting errors in the timestamp value. The timestamp parameter is used to ensure the validity and security of the request, so it is crucial to include it properly.
