After a day spent researching, this seems to be the damning line from Apple: The following app behaviors are incompatible with App Sandbox...you cannot sandbox an app that controls another app. Link. I do not know the inter-process communication method the 3rd party SDK uses to talk to its partner app, but it's not AppleEvents. The interface is proprietary.My app already has "Accessibility" privileges turned on in the Security & Privacy control panel (it has to monitor the keyboard)...that works fine. I tried giving my app "Full Disk Access" and the SDK still will not connect to the partner app. I can find no other entitlement that applies in this case.Any suggestions?