Excerpt from the manual. Page 159
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If not, you are not completely connected. Check the following:
1. XPUIPC installed in X-Plane Plugins folder or FSUIPC installed in FSX/P3D
2. Make sure you are running the latest version (22.214.171.124 as of this writing)
3. English-US Language installed and set as Primary Language
4. Working Microphone installed and set as Default Sound Input device in Windows
5. Valid Call Sign – Try using the default call sign of Mfg: Beech; Tail Number: N431VB. Press the Save button.
6. Try running the program in Administrator mode by right clicking on the Pilot2ATC.exe file and selecting “Run as Administrator”
7. If connected but the radios aren’t working, check the Battery and Avionics switches on or the “Ignore battery” and “Ignore Avionics” options are checked in P2A Config
8. If it seems to partially connect but the Connect button does not turn Green, set the Weather option to a different source such as NOAA Real Time Weather and try again.