How to receive Itron ERT transmission

What do you mean by this? Receive on what?

At one point Digi manufactured some ERT gateways/bridges but they went EOL a while back and I’m not aware of any new releases that support ERT.

If you’re in possession of one of those old gateways you might find the following documentation helpful. If not, maybe contact Itron and see if they have any current solutions?