How to add a new line in a Xero invoice

[MareeW]

Hi. I am making a workflow that can add a new contact, check for existing invoices and add a new line to an existing invoice in Xero. I cannot get the last bit to work. The only Xero module that looks correct is the “Update an Invoice” module, but it replaces the existing line with a new line, I want to add another line. How do we do this?