Ewa here from the Engineering Team at FreeAgent — I’m sorry to hear you’ve had some trouble and I’ll do my best to help out.
I’m afraid at present our API will return the
written_off_date only if there are no existing payments associated with the invoice in question — which means it will only get returned for invoices which have been fully written off. I realise this is not ideal, so I’ve added support for the
written_off_date on part written-off invoices as an improvement request to our public FreeAgent API Development board here: https://trello.com/c/cwPRSywA/60-return-writtedoffdate-for-part-written-off-invoices.
I hope that clarifies things for you Jon, but please let me know if you have any further questions.