Troubleshooting:
Q. I can't upload my custom voice prompts, or they do not play. But voice prompts work if I record them from the phone.
Solution:
The WAV file you uploaded is not in the correct format. Voice prompts must be in this file format: 8000 Hz, mono, 16-bit, PCM, .wav, 2MB max.
To check it (in Windows), right-click on the file and select "Properties...". Select the Summary tab, and click the "Advanced >>" button. Refer to the screenshot on the right.
For tips on correcting this, please see: u. Editing WAV/MP3 files with Audacity