Speefusion active but only one LTE at a time

I am testing a Pepwave MAX HD4 + Balance 310 combination : I send a MPEG-TS stream from an H264 encoder connected to the MAX HD4 to my public IP (dest. TCP/9123). On the web interface, I see that only ONE SIM card is used at a time, even if the Speedfusion is correctly configured (Speedfusion tests launched from the web interface effectively use the 4 SIM cards).
The traffic is NOT distributed amongst the LTE connections.
Topology:
The Balance is behind a firewall + NAT (ports TCP/32015 and UDP/4500 forwarded) with IP 10.60.1.6/24 (connected to WAN1).
The decoder that receives the video stream is on the same LAN : 10.60.1.28/24
The firewall fowards the video stream to the decoder (TCP/9123).
Am I missing something with SpeedFusion?
Thank you

Is the Balance deployed as drop-in mode? The decoder needs to be on the LAN side of the Balance and the stream should be sent to the 10.60.1.28 private IP.

From the description it sounds like it is not going through the VPN and you can confirm this on the HD4 under: Status> Active Sessions.

In the user manual, I had understood that drop-in mode was just an option to make the setup easier and that I could follow the “13.2 The Peplink Balance Behind a NAT Router” instructions instead.
Furthermore, according to the video tutorial, in drop-in mode, I should assign another public IP address to the Balance but what if my ISP just provides me one public IPv4 address?
Finally, if I put the Balance in drop-in mode before my firewall, how can it access the decoder which sits behind the firewall? (taking the decoder out of my internal network to plug it to the Balance is not an option since other devices in my LANs need to access it too )
Thanks

Drop-in mode is an option to make the setup easier but you can follow the “13.2 The Peplink Balance Behind a NAT Router" instructions instead.

The decoder remains inside your internal network. The H264 encoder on the LAN side of the HD4 would point to the private IP of the decoder through the VPN as there is no NAT when going through SpeedFusion.

Thanks for your help, it works fine now.
I thought that as soon as the Speedfusion VPN was up, all the traffic was automatically redirected to the VPN but now I understand it works as a “standard VPN” with pushed routes.
Regarding my stream, I usually send MPEG-TS over UDP on dedicated network and TCP when going through public internet (loosing packets causes image degradation). In the case of the Speedfusion link, do you think UDP could be used reliably?

SpeedFusion has features such as WAN smoothing to make it more reliable and you can also enable the RX buffer on the receive side to help.