Four limits, and the fourth one keeps quiet
Three CSV upload conditions fail loudly: the file exceeds 350 KB, runs past 1,000 rows, or has five columns where the form wants three or four. You split it, delete columns and try again. The fourth is the date. Upload instructions ask for dd/mm/yyyy, while a US statement uses mm/dd/yyyy, so 03/04/2026 can arrive as the wrong month. The .qbo route carries each date as one unambiguous field.