facebook - No request parameters received in "local payments" real-time updates callback -

i'm implementing new "local payments", , have subscribed real-time updates "actions" on "payments".

my callback url pinged ok when payment made, has no request parameters set @ (neither post nor get) - doesn't contain "verify token"!

(note: receive request parameters when first setting subscription ("hub challenge" etc) once live , being notified payments, no request parameters come through @ all.

anyone else problem or know how fix it?

thanks!

[update: solved!]

figured out - expecting values sent http request parameters, sent json-encoded in body, documented here: https://developers.facebook.com/docs/reference/api/realtime/