As other folks have indicated, there can only be one master making requests via RS485/Modbus (RS485 refers to the mechanism by which the signal goes over the wires and Modbus refers to the protocol) at any one time.
Modbus is a request/response protocol where the master always initiates each exchange. It does this over RS485 by setting the A and B pins of the RS485 connection to high or low voltage values to communicate the bits of its request. If two masters tried to send requests at the same time, they would combine to create a nonsense signal that no slave would be able to respond to. Similarly, a slave sets those same A and B pins voltage values to respond - so if a second master tries to make a new request while a slave is sending a response, the response will become corrupted.
Fortunately, Modbus requests/responses include a checksum - data included in each message to help validate that the payload of the message matches what was intended to be sent. This means that the most likely failure mode is requests/responses which are seen as corrupted and discarded. Depending on the systems involved, this might impact every request or only a rare request here and there.
I expected to plug them both in to provided ports, but, no. So, I found this, refreshed my recollection of RS-485, searched Amazon, and found this, which I think will work:
https://www.amazon.com/gp/product/B07CW7JHYV/
That would physically work, but will result in corrupted/discarded messages. Don't do it this way if you want your system to work reliably.
Customer service says I can do it if I use a 1m2s adapter.
Yes, I believe this device works by acting as a master itself when talking to the SCC (Epever Triron), then in turn acting like a slave when talking to each of the other masters. It receives requests from each master and proxies them to the SCC - making sure that only one request is active at a time to the SCC. None of the requests collide or get corrupted because there are three separate RS485/Modbus connections - one each from the masters to the 1m2s adapter and one from the 1m2s adapter to the slave(s).
If you don't want to buy the 1m2s adapter you could implement your own system to proxy requests from one or more masters.
I did this for a while using a Raspberry Pi so I could have the MT-50 connected while still gathering metrics with my custom code on the Raspberry Pi. The setup is roughly described in the first part of [this blog post](https://symbioquine.net/2020-10-27-epever-esp-8266-controller) and the code was something like what I've linked to in
https://diysolarforum.com/threads/s...ever-controller-with-python.25406/post-300209
https://gist.github.com/symbioquine/00b3884b2d41ce69edb3547112706289