[A] In a transaction, it may happen that an invoice is created by a counterparty.
[B} If an invoice has been created by the counterparty who is also using TranZact then only they can cancel the invoice created by them.
[C] You can request them to cancel the invoice using post comment section
[D] If the invoice is not created by the counterparty and still you are not able to cancel the invoice then please check if the payment is logged against that invoice or not.
[E] If the payment is logged against that invoice you will have to cancel it first then you can cancel the invoice.
Keywords - Cancel Invoice, not able to cancel invoice