Is there any endpoint to delete an invoice from account using sage financial api?
Thanks for your question.
There isn't an endpoint for Financials for deletion. You'd need to use the standard Salesforce API to do this with multiple actions i.e. unpost the transaction(s) then delete the object.
There is a DELETE endpoint. It is documented here and allows you to void an invoice. Although this is available, no record in Sage should ever be "deleted". So, Sage only voids the invoice when you call the DELETE method.