Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
It is possible that if you were not using the exactly right XLR microphone adapter it would not work with the A7S camera.
The right one would appear to be this:
However, if you were using that adapter with the wrong microphone or the wrong sort of microphone plugged into it, the result might be an error message from the camera, not about the adapter being incompatible, but about the microphone plugged into it. So please let me know what microphone you are trying to use. Thanks.