Grain's recorder relies on a Zoom setting called “Local Recordings” to record your call. This setting can be set on the Zoom team and user account level.
Turn on the Zoom setting "Local Recordings"
Step 1: Access your Zoom team or Zoom personal settings, found here
Step 2: Go to the "Recording" tab
Step 3: Turn on the account setting “Local Recording”
Step 4: Check the box for “Hosts can give meeting participants permission to record locally”