Bambora process_transaction.asp error: "Declined: Entered Information Cannot Be Authenticated"

If you are using Bambora's (formerly Beanstream) process_transaction.asp and receive the error "Declined: Entered Information Cannot Be Authenticated", you may find this frustrating, because although this error appears in their documentation, there's no information about what it means or how to solve it, which is basically useless.

At least one reason this error can appear is if the hashValue variable is not included in your query string.  To make it, use code similar to the following:
$query_string .= "&hashValue=" . sha1($query_string . $your_hash_key);
It may be worth it to note that not only is this error message completely undocumented, the hashValue variable does not appear in the Querystring API documentation.

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