Four limits, and the fourth one keeps quiet
Three of the CSV upload conditions fail loudly. The file is over 350 KB, or it runs past 1,000 rows, or it has five columns where the form wants three or four. You split it, you delete columns, you try again. The fourth condition is the date, and that one does not fail at all. The upload instructions ask for dd/mm/yyyy, a US statement spells it mm/dd/yyyy, and a row dated 03/04/2026 arrives as the wrong month inside a batch you have already ticked off. The .qbo route carries each date as one unambiguous field, so there is nothing left in it to interpret.