For 2-channel audio, the bitrate = 128 kbps; 1-channel = 61 kbps. This-
in addition to ffprobe and mediainfo characterizations-confirm that audio stream is MP3/LAME-encoded, though files come down with an ".mp2" extension.
Here is mediainfo file characterization output for the encoding settings:
Encoding settings : -m m -V 5 -q 0 -lowpass 17 --vbr-mt -b 32
Encoding settings : -m j -V 5 -q 0 -lowpass 17 --vbr-mt -b 32