How to manage a single Network in two physical locations?

Alright, my first time here and i'm bashing my head against a wall.

I have a customer, that has Server in our Datacenter and on location. Both share the same /24 Network. Between those is a Sophos XG in our Datacenter with a direct link to a router on the customers end.

Our Firewall is able to reach devices on the remote location. None of the servers in our location can though. If i set a static route that sets the Firewall as Gateway for a specific Address of one of the "remote" Servers, it works.

How can i make this work? From my understanding, Servers at our location don't reach the remote Servers, as the traffic would need to be routed through the Firewall, even though it's the same network. Since it's the same network though, the Server doesn't send the traffice to the Gateway when no specific static route exists.

Since we are talking 150 Servers +, is there any Solution that doesn't involve writing 300 or so static routes? I'm not that great when it comes to networking, so i might miss something obvious here.

After further evaluation i'm pretty sure subneting is the solution here. I don't think communication on the same network split by anything can work that way and the /24 Subnet needs to be divided per location and then routed properly.