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Hereby is used in connection with what is present with the speaker or what the speaker has just mentioned or the speaker's present words (i.e. the present document); thereby is used in connection with what is at a distance from the speaker or what has been mentioned by the speaker or by someone else.
Both usages are incorrect since hereby is an adverb but you are attempting to use it as an adjective. Also that is not a sentence as it lacks a verb. It is a subject (The total amount) with a long prepositional phrase (specified in..) with a nested prepositional phrase (attached to...).