Currently only 128 bytes per package are captured when running flow-accounting.
Add new CLI option set system flow-accounting packet-length <n>. This defaults to 128 if unset so it keeps beeing backwards compatible.
From the manual:
Specifies the maximum number of bytes to capture for each packet. This directive has key importance to both classification and connection tracking engines. In fact, some protocols (mostly text-based eg.: RTSP, SIP, etc.) benefit of extra bytes because they give more chances to successfully track data streams spawned by control channel. But it must be also noted that capturing larger packet portion require more resources. The right value need to be traded-off. In case classification is enabled, values under 200 bytes are often meaningless. 500-750 bytes are enough even for text based protocols. Default snaplen values are ok if classification is disabled.