Arduino GSM Shield 2 - Microphone not working

Hi together,

I´ve a Arduino GSM Shield 2 connected to Arduino UNO. Everything is working fine except the microphone Input on the Audio jack.

I´ve managed to Setup and receive Audio calls. I Can hear the caller but I can´t response because the microphone Input does not seem to work.

Is there someone who could help me solving this problem.

Thank you in advance for your help. Kind Regards