Just send it. Separate money orders are as good as a single one.
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USCIS shouldn't care, as long as both money orders together total $680 and can be traceable to your N-400 application.
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My colleagues are correct - as long as both money orders are in the same package, it is fine. Optimally, both should have your name and "N-400" on the reference line.
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It does not matter as long as the total amount is correct.
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