Bash multiline heredoc

cmdRes=$(/usr/bin/curl -s --request POST "https://wap.tplinkcloud.com/?token=$TOKEN HTTP/1.1" \
    --header "Content-Type: application/json" \
    --data @- << REQUEST_BODY
{
    "method":"passthrough",
    "params": {
        "deviceId": "$DEVICE_ID",
        "requestData": "{\"system\":{\"get_sysinfo\":null},\"emeter\":{\"get_realtime\":null}}"
    }
}
REQUEST_BODY
)