You said no to a permission and need to undo it
macOS asks for the microphone exactly once. Say no and the prompt never returns, so the only way back is System Settings. System Audio Recording is never asked for in advance at all, which means a refusal shows up as a recording with nothing on the other side rather than as a dialog you can answer again.
Put it right
Section titled “Put it right”-
Open Settings (⌘,) and select Advanced.
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In the Permissions section, find the row that does not read Granted.
If System Audio Recording reads Required. macOS asks the first time you record a call., Recordstead has not recorded since it last opened, so the row cannot tell yet. Make a short test recording, then check again.
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If it reads Denied. Click to open System Settings., click Open System Settings in that row. Recordstead opens the matching pane in System Settings for you.
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Switch Recordstead on there.
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Come back to Recordstead. The Microphone row updates as soon as Recordstead regains focus. The System Audio Recording row keeps its last result until your next recording starts.
For the Microphone, the pane is System Settings › Privacy & Security › Microphone.
For System Audio Recording, use the row's Open System Settings button rather than looking for the pane yourself.
When it says Granted and the other side is still silent
Section titled “When it says Granted and the other side is still silent”System Audio Recording reads Granted once a recording has started capturing. If the other side is still silent, switch Recordstead off for System Audio Recording in System Settings › Privacy & Security, switch it back on, and make a short test recording. If this happens straight after an update, tell support.
Result
Section titled “Result”The Microphone row reads Granted, and after your next recording starts, so does System Audio Recording. That recording has both sides in it.