Related param is ignored when trying to access api through event script

Thank you todd, adding it directly to the url works.

one extra question, how can i append related param in pre-process GET script, i tried using event.request.payload.resource[0].related, but it failed?

event.request.payload.resource[0].related = [{"name":"voucher_redemption_by_voucher_id"}];

error retuned

Cannot read property '0' of undefined

thanks again