When using the App Store Connect API to request sales reports, the date format depends on the frequency of the report. For monthly reports, the format should be YYYY-MM, whereas for daily reports, the format is YYYY-MM-DD. For yearly reports, the format should be YYYY.

If you request a monthly report but use the YYYY-MM-DD format, it may result in an error due to an invalid combination of frequency and date format​ Apple Developer

So, for your monthly and summary reports, ensure you're using the YYYY-MM format.