On some versions of Unreal Engine 5, the default entitlements used by Unreal Engine for some build types of sandboxed apps are missing the required support for network communication (entitlement com.apple.security.network.client). This makes the operating system to discard all the messages sent by the plugin. The solution is to simply add the required missing entitlement.

Options for the used entitlements can be found under Project Settings > Platforms > Xcode Projects, section Entitlements:

• Mac: Development Entitlements, set to /Game/Build/Mac/Resources/Sandbox.Server.entitlements
• Mac: Shipping Entitlements, set to /Game/Build/Mac/Resources/Sandbox.NoNet.entitlements

You must ensure the used entitlements files contain the following snippet:

<key>com.apple.security.network.client</key>
<true/>

For example, this is a minimal change of file Build/Mac/Resources/Sandbox.NoNet.entitlements for UE5.3.2 that makes the communication working:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>com.apple.security.app-sandbox</key>
    <true/>
    <key>com.apple.security.network.client</key>
    <true/>
</dict>
</plist>