To send APNS, define the service in Blk:
"Apple" : { "Cert": string "Key": string "Passphrase": string }
where the parameters are described here. Then in the request where you want to send APNS, define key _gapple in the output data structure other:
"_gapple": { "Device_token": string, "Badge": int, "Sound": string, "Content": string, "File": string, "Extra": {key: value, key: value, ...}, key, value, key, value }
Again, Content is the alert body which can constructed from File and Extra too.