Invoice cannot be deleted. Bill payment found. Please delete payment first.

Amicus Billing does not permit users to remove or delete an invoice when a payment or payments are posted against the invoice being deleted.

Note all payment details for the Bill being deleted, as they will need to be re-entered when the bill is recreated.

Open the File where the invoice being deleted is located and switch to the Billing side of the File.
Select Bills.
Set the Bill Detail window on the top, to Show: Paid & Outstanding.
Select the Bill and expand to see the payment(s) on that bill.
Select the payment then right click select Delete to remove the payment.