I have slowly gone crazy over the week, please help!

I have a recurring payment setup with Stripe - and I want some customised action on 'frm_payment_status_complete' when a new recurring payment comes in...

how do I grab the entry id of the original recurring payment from the API message from stripe? I have tried every combination, i thought it would be [payments]->item_id but this is blank. have tried all sorts but nothing is working. Thanks!