How can you connect with every server in studio?

For example lets say i crate a system people can buy furniture and then sell it with a gui he can put the money he wants for it and people can buy it on every server. So they can purchase in any server. But id don't know how to do that. If u know about it please help.

You can use messaging service to send messages across servers.

You can send the purchasable furniture in the message and then have the purchaser send a message back explaining that they bought the item.