Let's say you have an open manual invoice and you receive payment externally, which you will need to record in the invoices within your Recurly UI.
If we look at the sample invoice below, we can see that there is an option to enter a Date in the 'Record External Payment' section of the invoice:
As you can see, I can add a date of October 15, 2019 in that field, but if I post it today, the Transactions export would display today's date (which is October 22, 2019), not the date I entered in that field.
So, if I download the Transactions export for October 15, 2019 expecting to see the transaction entry above displayed, this will not be the case. The reason for this is that the Transaction export is based off the transaction creation date not the date entered for manual payments. Therefore, the manual transaction I entered above will appear in the Transactions export for October 22, 2019, not October 15th.