You can have the Server start before the connnection to the Remote counterpart has taken place by configuring a "robust" Proxy Adapter (see the example in DOCS-SDKs\sdk_adapter_remoting_infrastructure\conf\sock ets(robust) ).
In this case, the startup behavior is governed by the "missing_connection_timeout_millis" parameter supplied to the Proxy Adapter.

I confirm that the presence of some connected client is needed in order for the Remote Data Adapter to to anything useful;
but in the meantime the Server has no reason for closing the connections. Until the first client subscribes to anything, your PHP code should be waiting on fscanf.
Please specify the error message issued.