If you're using a non Faststream codec headphone (like Bose, Sony, Apple headphones, they don't support Faststream codec), C81 can auto switch to talk mode on most Windows computers and Macbook. But on PS4/PS5, you need to switch it to talk mode manually if you don't use the small Mic (Use the 3.5mm Mic on PS4/PS5). Please double click the MFB button on C81 to switch it to talk mode. In call mode, LED light on C81 will be solid White.
If you still can't get the mic to work once you switch C81 to talk mode, please check as following:
Step 1: Make sure you have set the sound setting well. Adjust the Sound Setting on Audio source.
Step 2: Sometimes you need to adjust the settings again in the app itself like Skype. Make sure the input device has been set to the Avantree Adapter.