daily receipts

You can reopen the period in your settings, then period, reopen there. Be careful with your return, though. If you have already submitted a return for that period, it will no longer be correct. And I've heard that you can no longer submit a corrected return.

Thank you for your answer, I had found it in the meantime... I just had to fill in the last 'empty' days from the previous quarter with 'no income that day' in order to be able to fill in the next quarter. As long as there were still empty days stated in the previous quarter, it didn't succeed, apparently. But in terms of income, nothing changes, so luckily (hopefully) it doesn't make any difference in terms of the return.