Hey @Spider100! It certainly sounds like you are doing everything correctly for this to complete. The 4 inch distance is well within the 6 inch recommendation. Please also ensure the microphone on the listener is facing the smoke/ co alarm.
Check out our help center article for more tips for testing and setup the Smoke/ Co Listener.
If this concern persists despite checking the above information, please give our support team a call at one of the numbers available here. We’re taking additional steps to protect our team and help reduce the spread of COVID-19, so this has resulted in longer than normal wait times. If you are outside of the US, please read our response to COVID-19 here to see how to contact support.