Hi @gmu
Do you have any other data on your account that you need to keep? You can’t delete invoices completely, unless you clear your account.
If you have data you need to keep (e.g. real invoices), you may wish to undelete the invoices, renumber them and re-delete them (prefix them with something like “TEST”).
The reason we don’t allow invoices to be completely deleted is for auditing purposes. HMRC likes continuous numbers, and if there are gaps, you have proof on why they are there.
Hope that helps