In Teamleader you can only delete the very last invoice of every fiscal year unless it’s a pending invoice (not booked yet).

The underlying reason for this is that the automatic numbering of the invoices would be mixed up otherwise. This in turn is related to the rules of accountancy, which state that invoices should always be chronologically ordered. If you want to delete an invoice, but other invoices have been booked after that one, you will need to delete every invoice up to that date.

For this same reason, the same applies to credit notes.

You can delete the invoice by hovering above the arrow on top and clicking 'Delete'.
Note: When deleting an invoice this info is irretrievably lost

It is not possible to delete invoices in bulk, but there is, nevertheless, a small trick that you can still do: 

If, for example, you need to delete the invoice 2017/134 and you have already created the invoices 2017/135, 2017/136, 2017/137 etc... you can follow these steps:

1.  Make copies of all these last invoices (numbers 2017/135, 2017/136, 2017/137...) so that they are duplicated and saved as pending invoices. (On the arrow mentioned above > Create copy).

2. Delete one by one the booked ones (so number 2017/135, 2017/136, 2017/137...) and the one that you really wanted to delete (so, in this case the number 2017/134).

3. Go back to the pending invoices that you just created, and book them so that they receive a number. 

Note that by doing this you will lose the tracking of all the invoices that you have deleted, (the date when you sent them, the number, the payment status, reminders etc...) so we recommend that you follow this workaround only if you are sure that you can do this.