Otter.ai app not working

Hi there! I work for a disabled students program at a community college. I introduced a student to an app called Otter, which uses the iPhone's mic to record and transcribe text. When he tried to activate the recording feature on his phone, it doesn't work, and he receives a message that says, verbatim: "iOS doesn't allow recording while a phone call is in progress". The problem, of course, is that there is no phone call in progress. In order to verfiy this, the student turned on his app switcher and closed any apps that were running in the background, including his phone app. We also tried uninstalling and reinstalling the Otter app, but we still get the same message.

The student is hard of hearing, but he doesn't know of any phone settings he's using that might be convincing his phone that he's on a call. I looked at his settings, but I'm not sure what to look for. We gave Otter permission to use his mic, but that doesn't seem to be the issue, anyway.

Has anyone experienced this "error" message before? Any help would be greatly appreciated. Thank you so much.

Nate