React native ffmpeg producing unplayable hevc videos that still have audio

Question

I have a react native application that is attempting to transcode users videos so they are in a format both platforms can natively playback, we are doing it on device for now as we don't want to incur the API costs till we have a stable user base. I have a few questions and let me preface them with my ffmpeg knowledge is not the best and mostly cobbled together.

1. Why does the following code produce videos that are unplayable but still have audio.

if (Platform.OS === 'ios') {
      await FFmpegKit.execute(`-i ${path} -c:v hevc_videotoolbox -c:a aac -movflags +faststart -y ${outputPath}`);
} else {
      await FFmpegKit.execute(`-i ${path} -c:v hevc_omx -c:a aac -movflags +faststart -y ${outputPath}`);
}

2. Is there a better set of commands to run for 1080p videos that will be played back on both platforms?

I am getting ffmpeg into the app using https://github.com/arthenica/ffmpeg-kit and am using the min-gpl distribution. If I set the commands to use their h264 alternatives for the codec (h264_videotoolbox & h264_omx) it produces working files but I was hoping to use hevc to minimize the file sizes.

Update - Solved

The -tag:v hvc1 needed to be added so that Apple players can play the HEVC content.