Delete Invoice Entries
When you delete an invoice in Time Tracker, there is an option whether or not to delete invoice entries together with an invoice with a default action set to
do not delete.

Delete invoice entries option in Time Tracker
Invoice entries are items that are included in the invoice. They are either
time records or
expenses.
Deleting invoice
without deleting entries removes the invoice but
keeps the items in the database. Deleting invoice with entries also
deletes all included items.
Time Tracker User Guide