Hi,
It sounds like you are using Mikrotik routers for your hotspot setup and you are currently using a bridge to enable switching between the LTE and WiFi interfaces. You mentioned that the issue is that the traffic is being masked behind the virtual MAC on the bridge, which is the same on all the routers, and that this is preventing the 3rd party portal provider from providing individual reporting.
One way to resolve this issue without using a bridge would be to set up VLANs on each router, as I mentioned earlier. You can assign the WiFi interface to one VLAN and the Ethernet interface to another VLAN. This way, the traffic on each interface will be separated and the 3rd party portal provider will be able to distinguish between them.
Another option could be to use the slave-port feature on Mikrotik, you can use it to enslave the WiFi interface to the Ethernet interface. This will allow the traffic to pass through the Ethernet interface but still be able to use the hotspot on the WiFi interface.
You can also look into internal routing to allow switching between interfaces without the bridge, but that would depend on your specific setup and the level of routing knowledge you have.
In any case, since you are not a Mikrotik expert, it might be a good idea to consult with a network administrator or a Mikrotik certified professional to help you with the configuration and ensure that the network is set up correctly.