We default the date of your invoices to the day that you first start working on the invoice, so if you take a few days to draft one from start to finish, don't forget to update the invoice date before you send it.
Simply head to your Invoices tab > tap on the relevant draft invoice > scroll down to amend the date.
Read more:
Automatic matching of your invoice payments (and how to mark invoices as paid)
Manage your invoices (see which invoices you've got paid, unpaid, late or unsent)