My file has dates that do not exist
A date column contains days that are not on the calendar: a 31st in a thirty-day month, or a 29 February in a year that has no such day.
Why it happens
- Hand entry is the first source.
- A swapped day and month is the second and more insidious source.
- Leap years are the third.
- The cost is downstream rather than here.
What to do now
- Check the day against the month rather than against 31.
- Treat an impossible date as evidence about the whole column, not as one bad row.
- Go back to the sender for the real value.
Next time
A date field checks that the day exists in that month, in that year, so 31/02/2026 is refused and named rather than exported as “2026-02-31” for something downstream to choke on.
Start from the invoice line items template.
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