About The audio loop of AT command

I want to use the AT command AT&T1 to make the audio loop test,but it does’t work.the AT Command Interface Guide.pdf said that:

The audio loop activation (enabled with AT&T1 command, disabled with AT&T2 command) involves
some restrictions on the use of other AT commands.

  • Audio loop mode must not be enabled when a communication is active.
  • Audio loop mode must not be enabled when a tone is under generation
  • Audio loop must be disabled (if active) Before opening a communication
  • Tone generation and sidetone modification must not be possible when the audio loop is active.

what does communication mean? And what does “a tone is under generation” mean?

Any help would be appreciated!

I use Q2687

I think it means, “a call is in progress” :question:

“A tone is currently being generated” :question:

But I have tried to send the AT&T1 to Q2687 before I made a call, the audio loop still didn’t work the same.
I have tired to send the AT&T1 before a call, or when the Q2687 was ringing ,or when a call is in progress.