Chrome Failed to Start Native Messaging Host on Mac - google-chrome

Question

Just to preface, I'm very new to all of this so please let me know if I'm missing anything fundamental or if I'm even going about this the right way.
I'm trying to make a chrome extension that reads the sender of an email in Gmail, then starts a python script (fmconnect.py) and sends the name of that sender to the script. I am able to retrieve the name of the sender using gmail.js, but when I try to send it to the python script, I keep receiving the error:
Unchecked runtime.lastError: Failed to start native messaging host.
Here are all the relevant files:
background.js
chrome.runtime.onMessage.addListener(function(request, sender, sendResponse) {
console.log(request);
sendResponse({message: "Message received"});
if (request.length > 0) {
const hostName = "com.google.chrome.example.echo";
var port = chrome.runtime.connectNative(hostName);
if (port) {
port.postMessage({text: request});
}
}
return true;
});
relevant part of manifest.json
"permissions": [
"https://*/*",
"http://localhost/",
"nativeMessaging",
"background",
"tabs"
]
fmconnect.py
def read_thread_func():
text_length_bytes = sys.stdin.read(4)
sys.stdout.write(text_length_bytes)
def Main():
read_thread_func()
sys.exit(0)
if __name__ == '__main__':
Main()
com.google.chrome.example.echo.json
{
"name": "com.google.chrome.example.echo",
"description": "Chrome Native Messaging API Host",
"path": "HOST_PATH",
"type": "stdio",
"allowed_origins": [
"chrome-extension://xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/"
]
}
install_host.sh
set -e
DIR="$( cd "$( dirname "$0" )" && pwd )"
if [ "$(uname -s)" = "Darwin" ]; then
if [ "$(whoami)" = "root" ]; then
TARGET_DIR="/Library/Google/Chrome/NativeMessagingHosts"
else
TARGET_DIR="$HOME/Library/Application Support/Google/Chrome/NativeMessagingHosts"
fi
else
if [ "$(whoami)" = "root" ]; then
TARGET_DIR="/etc/opt/chrome/native-messaging-hosts"
else
TARGET_DIR="$HOME/.config/google-chrome/NativeMessagingHosts"
fi
fi
HOST_NAME=com.google.chrome.example.echo
# Create directory to store native messaging host.
mkdir -p "$TARGET_DIR"
# Copy native messaging host manifest.
cp "$DIR/$HOST_NAME.json" "$TARGET_DIR"
# Update host path in the manifest.
HOST_PATH=$DIR/fmconnect.py
ESCAPED_HOST_PATH=${HOST_PATH////\\/}
sed -i -e "s/HOST_PATH/$ESCAPED_HOST_PATH/" "$TARGET_DIR/$HOST_NAME.json"
# Set permissions for the manifest so that all users can read it.
chmod o+r "$TARGET_DIR/$HOST_NAME.json"
echo "Native messaging host $HOST_NAME has been installed."
I know that on the native messaging host documentation, it says to check whether I have sufficient permissions to start the file. How exactly would I do this?