So the error shown under the URL you have originally shared wouldn’t be coming straight from the n8n instance (as it would throw an error like {"code":404,"message":"The requested webhook \"GET foo\" is not registered ... instead). I do however wonder if you are affected by the problem described here:
Could you try the approach suggested by @ivov in the linked thread to see if that changes the behavior for you here? So deleting the tunnelSubdomain key from your ~/.n8n/config (Mac) or C:\Users\Username\.n8n\config (Windows, replace username with your actual username) file, changing the file content from something like this:
{
"encryptionKey": "foo",
"tunnelSubdomain": "bar"
}
to this:
{
"encryptionKey": "foo"
}
Make sure to quit n8n.desktop beforehand and restart it afterwards.