Start by looking at the valid/invalid counts on the review screen — every checked row needs to pass before anything can be saved. The things that trip people up most often: dates written in a different calendar than expected (these get left blank rather than guessed, so you'll need to fill them in), rows that were skipped because their date or amount could not be read (a notice shows how many), and a balance column that doesn't quite line up with your amounts (this is just a heads-up, not a blocker — you can still enter your opening or closing balance by hand).
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