RC7620 Loopback


I would like to perform a loopback test with the RC7620.

A forum page, RC7620 audio distorted,
shows that it is possible.
However, the command that activates the loopback “AT!AVAUDIOLPBK” is not in the AT command reference manual that I have ( Rev. 6.0). Is this functionality no longer supported or am I using the wrong document?
Any input would be appreciated.

Thanks in advance

you can see this updated document: