Only PCM encoded, 16 bit, mono, 8kHz/16kHz files are supported with a lowercase ‘.wav’ extension

 Only PCM encoded, 16 bit, mono, 8kHz/16kHz files are supported with a lowercase ‘.wav’ extension

The file extension “wav16” can be used for 16kHz wav files.

https://community.asterisk.org/t/question-about-playback-audio-formats/83928