Hello Ron140, did you manage to save the invoice? Additionally, when you say cancel an invoice are you trying to delete or void it?
Saving the invoice enables the More actions button at the bottom, while the X button cancels an unsaved transaction.

If the bottom of your window is cut off, try adjusting your browser zoom settings or display settings to bring the buttons back into view.
When deleting or voiding an invoice, remember that voiding a transaction maintains a record of it with a zero balance, while deleting it removes the entire history and reverts the invoice to an unpaid status.
For record-keeping purposes, voiding is recommended over deleting because it maintains a record of the transaction in your records without affecting your totals.
If you mean something else, don't hesitate to revisit this thread.